问题描述：
on one of these ___ he went up the mountain accompanied by old peeper,the town optician ,who witnessed the failure.peeper encouraged bobby to try again and he presented him with a pair of special sunglasses.
A experiment B occasions
the answer is B,why not use
A experiments 忘记写S了
A experiment B occasions
the answer is B,why not use
A experiments 忘记写S了
问题解答：
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