Final answer:
The correct form to complete the sentence is 'saw', as in 'What would Anthony say if he saw this extraordinary painting?', for a second conditional sentence describing an unreal situation.
Step-by-step explanation:
The student is tasked with completing sentences by using the correct form of verbs in brackets to create conditional sentences. Specifically, for the sentence 'What would Anthony say if he _____ (see) this extraordinary painting?', the student needs to use the past subjunctive form of the verb because this is a second conditional sentence describing an unreal situation. Therefore, the correct form of the verb to complete the sentence is 'saw', resulting in the sentence 'What would Anthony say if he saw this extraordinary painting?'