A modifier question tests whether an opening describing phrase connects to the right noun. Start with the phrase before the blank, and ask who or what it describes. That phrase must describe the main noun right after its comma, even when other names appear later in the sentence. Then read through the words after the blank to check that the subject and verb work together. A sentence can sound natural while putting the noun the phrase describes in the wrong place.
Hints
- Hint 1
Look at the phrase before the comma. Who has examined the images and records?
- Hint 2
An opening describing phrase must describe the main noun right after its comma. Ask whether that noun examined the records, then continue into argue to check the subject and verb.
Step-by-step
Match the examiner to the subject
Step 1Identify what the opening phrase needs
The sentence opens with Having examined satellite images and meteorological records spanning fifty years, but it hasn’t yet named who examined them. Who must the blank supply? It must name the people who studied those sources and now make the claim about the desert, because an opening describing phrase describes the main noun right after its comma. The people doing the examining must also be the people making the claim.
- Step 2
Test the main noun, not names that appear later
What is the main noun at the start of each completion? In the rapid expansion of the desert, it’s expansion, which can’t examine images or records. In the conclusion reached, it’s conclusion; the people who reached it appear later, but their result can’t do the examining. The version beginning it has been argued uses an it that names no examiner, even though people appear after by. Naming the people later doesn’t make them the main noun after the comma, so none of these starts gives the opening phrase someone who could have done the work.
- Step 3
Read the matching subject through to the end
Put climatologists Diaz and Roe into the blank and read through to the period. Does this subject work with both the opening phrase and the words that follow? The two researchers are the main noun right after the comma, so Having examined describes them. The plural subject also fits argue, which leads straight into their claim about the desert’s expansion. Choice B.