The poet composed a poem while . . . . . . . . under a tree. A. sitting B. sat C. sit D. sits

The correct answer is A. sitting.

The other options are incorrect because they are not in the past participle form. The past participle form of the verb “to sit” is “sitting.” This is the form of the verb that is used after the auxiliary verb “to be” in the passive voice. In this case, the poet is the subject of the sentence, and the action of composing the poem is being done to him or her. Therefore, the correct verb form is “sitting.”

Here are some examples of how the past participle form of “to sit” can be used:

• The poet was sitting under the tree when he composed the poem.
• The poem was sitting on the table when I found it.
• I have been sitting here for hours, waiting for you.
• The children were sitting in the sandbox, playing.

I hope this helps!