The correct answer is A. laid.
The verb “lay” is used to describe the action of placing something down. In this case, the man is placing his camera down on the railing. The past tense of “lay” is “laid.”
The verb “lie” is used to describe the state of being in a horizontal position. In this case, the man is not lying down, so the verb “lie” is not correct.
The verb “lain” is the past participle of “lie.” It is used to form the perfect tenses and the passive voice. In this case, the man is not using the perfect tenses or the passive voice, so the verb “lain” is not correct.
The verb “to lie” is also used to describe the act of telling an untruth. However, in this case, the man is not telling an untruth, so the verb “to lie” is not correct.