Final answer:
The past perfect tense of the verb to plan in the given sentence is had planned (option B).
Step-by-step explanation:
The past perfect tense of the verb to plan in the given sentence is had planned (option B).
In the sentence, it states, 'Columbus _______ to reach Asia.' Since the action of planning to reach Asia is set in the past and completed before another past action, the past perfect tense is used. The correct form is 'had planned.'
An example sentence using the past perfect tense of to plan is: 'They had planned to leave for the vacation, but their flight got canceled.'