Read the paragraph. [1] thomas jefferson was the primary author of the declaration of independence. [2] jefferson began writing in early june of 1776, and he took three weeks to finish the first draft. [3] the delegates of the second continental congress reviewed the document during the last week of june. which is the best way to revise sentence 2 to improve sentence variety in the paragraph? in early june 1776, jefferson began writing, and he took three weeks to finish the first draft. jefferson, who began writing in early june 1776, took three weeks to finish the first draft. the first draft, which jefferson began writing in early june 1776, took him three weeks. jefferson took three weeks to finish the first draft, which he began writing in early june 1776.

Sentences 1 and 3 are both simple--they only have one clause--one subject and predicate.  To improve variety, sentence 2 should be a complex sentence that includes more than one clause. 
The first option best fits this complex structure:
"In early June 1776, Jefferson began writing, and he took three weeks to finish the first draft."

'In early June 1776" is a prepositional phrase--it describes "when" the writing took place.

"Jefferson began writing" is a complete, independent clause. Jefferson is the subject and 'began writing' is the verb phrase.

"he took three weeks to finish the first draft" is another complete, independent clause. He (Jefferson) is the subject still, and 'took' is the start of the verb phrase.

This second independent clause is separated by a comma and a conjunction word (and), which makes the sentence complex.