Answer:
D. swam
Explanation:
The correct option is the Past Simple verb because the verb climb is in the Past Simple too, which refers to past series of events that happen one after the other.
Option A is incorrect because the Past Perfect tense is formed with had and the verb in the past participle, like swum -so not it cannot be used with the past simple form. In alternative B the past participle swum cannot be used in the past simple form -it needs a perfect tense. Finally, swim is an irregular verb, so it cannot take the -ed suffix of regular verbs.
