Mr. Smith didn’t go to the party because he had a lot of experiments .A. doB. didC. doneD.

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A. do
B. did
C. done
(答案→)D. to do
解析：考查不定式的用法：句意：史密斯先生没有去参加晚会,因为他有许多实验要做。Have sth to do，有…事情要做，这里不定式做后置定语，修饰experiments，选D。