The correct answer is: B. could
The word “could” is the past tense of the verb “can,” which means to be able to do something. In this case, the question is asking whether or not the person was able to climb trees when they were young. The answer “could” indicates that the person was indeed able to climb trees when they were young.
The other options are not correct because they do not answer the question of whether or not the person was able to climb trees when they were young. The word “did” is the past tense of the verb “do,” which means to perform an action. In this case, the question is not asking whether or not the person performed the action of climbing trees. The word “how” is an interrogative pronoun that is used to ask for information about how something is done. In this case, the question is not asking for information about how the person climbed trees. The word “should” is a modal verb that is used to express obligation or necessity. In this case, the question is not asking whether or not the person was obligated to climb trees.