A verb form question tests whether the blank needs a main verb, which says what the subject does or is, or a form that only describes. Sort the forms of the same word into those two groups, then read to the period. Count the subject's main verbs, setting aside extra details. Every clause, a group with its own subject and verb, needs a main verb; a second one in the same clause needs a joining word.
Hints
- Hint 1
Read from archaeologists all the way to the period. Find the verb that tells what those people did.
- Hint 2
Check what would allow another main verb: is the blank in a clause with its own subject and verb, or in a list joined by a word like and?
Step-by-step
Find the main verb beyond the blank
Step 1Follow the subject to its main verb
Start with archaeologists and read to the period. Which verb tells us what those people did? The phrase aware that centuries of weathering can erase surface color describes what the archaeologists knew, so we can set it aside. After that detail, concluded tells us what they did. The subject already has its main verb, so we'll check whether the blank can add another verb or must describe the archaeologists.
- Step 2
Test whether another main verb is allowed
Can the blank add another main verb? No who or that before it opens another clause, and no and joins it to concluded. The helpers in were examining and had examined make them main-verb forms. Could examined describe the archaeologists instead? Add were to test that reading: archaeologists were examined microscopic traces. That doesn't make sense because the archaeologists examine the traces rather than being examined themselves. So examined also acts as a main verb here. Each form adds a second main verb without a joining word.
- Step 3
Choose the form that describes the archaeologists
What form describes the archaeologists doing the work? Examining is an -ing form without a helper, so it describes them rather than serving as a main verb. The phrase examining microscopic traces of blue pigment on several marble reliefs tells us what they were studying when they reached their conclusion. Choice C.