Spinelli v. Economy Stations, Inc., 71 Wn.2d 503, 508-09, 429 P.2d 240 (1967); Levea v. G.A. Gray Corp., 17 Wn. App. 214, 221, 562 P.2d 1276 (1977). See Kuster v. Gould Nat'l Batteries, 71 Wn.2d 474, 482-83, 429 P.2d 220 (1967). An erroneous assumption of a material fact destroys the probative value of a hypothetical question.

There is conflicting evidence on the issue of impairment but the court had the power to accept the testimony it did on which to base complained of findings. See Jacobs v. Brock, 73 Wn.2d 234, 437 P.2d 920 (1968); Kuster v. Gould Nat'l Batteries, Inc., 71 Wn.2d 474, 429 P.2d 220 (1967). The testimony of the school teachers and administrative personnel constituted substantial evidence sufficient to support the findings as to the impairment of the teacher's efficiency.

The trial court, however, on conflicting testimony, did not agree with the theory presented by the state and there is substantial evidenca in the record to support the findings of the trial court. Hernandez v. Western Farmers Ass'n, 76 Wn.2d 422, 425, 456 P.2d 1020 (1969); Kuster v. Gould Nat'l Batteries, Inc., 71 Wn.2d 474, 476, 429 P.2d 220 (1967); Johnson v. Ramstad, 68 Wn.2d 971, 413 P.2d 348 (1966). Without going at length into the supporting testimony substantiating the trial court findings, the record supports the trial court's conclusion that the Jaussauds-Sun-Glo option was never exercised, and that the conditions and figures for the property involved, therefore, had no relevance to the final purchase price and were rendered meaningless.

But in so doing he is not compelled to meet conjecture or mere possibilities with proof to the contrary.' " (emphasis added) (quoting Kuster v. Gould Nat'l Batteries, 71 Wn.2d 474, 485, 429 P.2d 220 (1967)). B. Superseding Cause Instruction

(emphasis added) (quoting Kuster v. Gould Nat'l Batteries, 71 Wn.2d 474, 485, 429 P.2d 220 (1967)).

But in so doing he is not compelled to meet conjecture or mere possibilities with proof to the contrary.Potter, at 752 (quoting Kuster v. Gould Nat'l Batteries, 71 Wn.2d 474, 485, 429 P.2d 220 (1967)). The Drivers contend that they offered competent expert testimony to establish that offgassed chemicals more probably than not caused the specified injuries.

The plaintiff is not required for purposes of defending against a motion for summary judgment to fend off defenses which have not been urged by the moving party. As stated in Kuster v. Gould Nat'l Batteries, 71 Wn.2d 474, 485, 429 P.2d 220 (1967): It is the law that the plaintiff must establish with reasonable certainty a manufacturing defect as a cause of the accident in order for him to recover damages from the defendant.

The Pearsons were not required to eliminate all other possible causes. Kuster v. Gould Nat'l Batteries, Inc., 71 Wn.2d 474, 429 P.2d 220 (1967). The jury was justified in drawing the reasonable inference that the arc in the cord came about as a result of a manufacturing defect.

[4, 5] Where the facts upon which a hypothetical question is based are subject to conflicting evidence, the answer to such a question is not rendered speculative or otherwise inadmissible providing that the question fairly incorporates the facts supported by evidence under the examiner's theory. Helman v. Sacred Heart Hosp., 62 Wn.2d 136, 150, 381 P.2d 605, 96 A.L.R.2d 1193 (1963); Kuster v. Gould Nat'l Batteries, Inc., 71 Wn.2d 474, 482, 429 P.2d 220 (1967). Furthermore, the trial court has wide discretion in determining the propriety of the hypothetical questions and answers and to supervise and control hypothetical questions.

We found liability in Lamphiear v. Skagit Corp., supra, where there were sufficient facts from which the jury could reasonably and logically infer that an accident occurred either of two ways. Either theory was plausible, and both were supported by sufficient circumstantial evidence from which reasonable minds could conclude there was a greater probability the accident occurred through a defect for which the defendant would be liable than that it occurred in a way for which the defendant would not be liable. Although Kuster v. Gould Nat'l Batteries, Inc., 71 Wn.2d 474, 429 P.2d 220 (1967), was decided before the landmark decision of Ulmer v. Ford Motor Co., supra, there are similarities that make that opinion of interest to our consideration of this case. In Kuster, as in this case, the record did not disclose any probable cause other than that testified to by plaintiff's experts.