During the summer months, the monastery . . . . . . . . very busy, for it is visited by thousands of people who . . . . . . . . the pass in cars.

The correct answer is: A. is

The sentence is in the present tense, so the verb “to be” must be used in the present tense as well. The other options are in the past tense, which is not correct.

The sentence also states that the monastery is visited by thousands of people, which means that it is currently busy. The other options do not accurately reflect this information.

Here is a more detailed explanation of each option:

• A. is is the present tense of the verb “to be.” It is the most common verb in the English language, and it is used to describe the state of being of a person, place, thing, or idea. In this case, it is used to describe the state of being of the monastery, which is currently busy.
• B. cross is the present tense of the verb “to cross.” It means to go over or across something. In this case, it would mean that the people are going over or across the pass in cars. However, the sentence does not state that the people are going over or across the pass, so this option is not correct.
• C. has been is the present perfect tense of the verb “to be.” It is used to describe an action that has happened in the past but has an effect on the present. In this case, it would mean that the monastery has been visited by thousands of people in the past, and this has made it busy in the present. However, the sentence does not state that the monastery has been visited by thousands of people in the past, so this option is not correct.
• D. have crossed is the present perfect tense of the verb “to cross.” It is used to describe an action that has happened in the past but has an effect on the present. In this case, it would mean that the people have crossed the pass in cars in the past, and this has made the monastery busy in the present. However, the sentence does not state that the people have crossed the pass in cars in the past, so this option is not correct.
• E. was is the past tense of the verb “to be.” It is used to describe an action that happened in the past. In this case, it would mean that the monastery was busy in the past. However, the sentence states that the monastery is currently busy, so this option is not correct.