71.

Answer and Explanation

Your Answer is

Correct Answer is B

Explanation

Before the underlined part "it takes a long time to wait for the right light...", after the underlined part "the moment the picture appears on the paper", so before should be used here. that guides the noun painting in front of the modification, and if the sentence is incomplete, it is wrong. as if seems to have the wrong meaning. Two complete sentences need a conjunction, D is wrong.