A verb form question tests whether the blank needs a main verb or a describing form. Sort the forms: a main verb tells what the subject does or is, but an -ing form needs a helper to do that. Then find the blank's own subject, reading past extra words between commas. When and joins verbs for that subject, match their form and tense unless a time clue places them at different times. A form can sound natural alone yet break this link.
Hints
- Hint 1
Read the words about the breakthrough. What links the verb in that part to the blank?
- Hint 2
For tense, check the time of the verb joined to the blank. Does the phrase about the following decades call for a change from that time?
Step-by-step
Follow the breakthrough's verbs
Step 1Find the blank's subject
Sort by job: securing can't be a main verb without a helper. Then look at a breakthrough that: that starts a clause, a subject with its verb, about the breakthrough. The blank belongs to this clause, so we need to check its verbs rather than Perlman's developed.
- Step 2
Follow the link made by “and”
What does and join? In transformed network routing and,, it joins the blank to transformed, which already tells what the breakthrough did. The breakthrough has a pair of main verbs, so their forms must match. The form securing would break this pair because it has no helper.
- Step 3
Match the past tense
The phrase over the following decades continues the story that starts in 1985. Which tense fits that story and transformed? The blank needs the simple past, the plain past form. The future will secure and the present secures shift away from that tense, while secured matches it. Choice C.