A verb form question tests whether the blank needs a main verb, the verb that says what its subject does or is. Sort the forms by whether they can be main verbs, then read to the period. A clause, a group with its own subject and verb, needs its own main verb. An -ing or to form can't supply that verb alone. Test the verb with its subject: it for one thing or they for more than one.
Hints
- Hint 1
Look at the words after the comma. What does that start, and does that part have a main verb of its own?
- Hint 2
Find the noun that that refers to. Does it name one thing or more than one?
Step-by-step
Find the blank’s clause and subject
Step 1Separate the two clauses
The biography already has a main verb in The biography of Ada Lovelace highlights. Does highlights also act as the main verb after letters that? No: that starts a clause, a group with its own subject and verb, about the letters. The blank belongs to that separate clause, so we have to check it for its own main verb.
- Step 2
Check for a main verb
Read that ______ the early development of computer science. to the period. What word says what the letters do? There's no other verb in that clause, so the blank must supply its main verb. An -ing form without a helper and a to form can't do that job, so documenting and to document leave the clause unfinished.
- Step 3
Match the verb to the letters
Which noun decides the verb’s form? In letters that, that refers to letters, which is plural, meaning more than one. The verb must match those letters, so use they document, not they documents. Choice D.