Complete the following sentence using the correct form of the verb in the bracket.
The historical monument _____ (built) thousands of years ago.
A) Was built
B) Were built
C) Is building
D) Is being built

Hint: By the correct form, the question means to say that we need to use the correct tense of the verb. Tenses are tools in English grammar which are used to express the time reference. These broadly include present, past and future tenses.

Complete answer:
In the given sentence, we are talking about an event that took place a thousand years ago. Here, the reference point is a thousand years ago. To talk about an event that took place before a reference point in the past, we use the past perfect tense.

Now let us analyze the given options:
Option A) was built – This option has the helping verb ‘was’ before the main verb ‘built’. This format of using verbs indicates that the sentence is in the past perfect tense. It means that the sentence is in the passive voice. Therefore, this option is correct.
Option B) were built – This option has the helping verb ‘were’ and the main verb ‘built’. This shows that the sentence is used in the past participle form. It is a correct way to write in the passive voice, but here it is wrong because the verb ‘were’ is for plural nouns and the noun used in the question is singular. Thus, this option is incorrect.
Option C) is building – The words ‘is building’ together indicate the present continuous tense. The sentence is talking about historical monuments and hence it should be in the past tense. Therefore, this option is wrong.
Option D) is being built – In this option the helping verbs ‘is’ and ‘being’ and the main verb ‘built’ together indicate that the sentence is in the present perfect tense. Again, we know that we are talking about a past event, and hence the tense should also be the past tense. Therefore, this is the wrong option.

Thus, the correct answer is Option (A) The historical monument was built thousands of years ago.

Note: The verb ‘build’ can be used in twelve different tenses. First are the three simple tenses i.e. build, built, will build. These are present, past and future respectively. When we write the perfect tense of these three tenses, they become has built, had built, will have built. And for the continuous tense, we use the -ing form of the verb. For e.g. is building, was built, will be building.