A punctuation question with different verb forms tests how a description fits into a sentence. Read the whole sentence and test each opening in it. Then check how the words connect: extra information needs matching punctuation at both ends, but a subject and its verb need no comma between them. Check verb forms too: an -ing form needs a helping verb to be a main verb, and two main verbs need a word to join them.
Hints
- Hint 1
The second sentence continues well past the blank. Read to the period and find the verb after the cave description.
- Hint 2
Look at the comma after “any one location” and ask what words that comma separates.
- Hint 3
Identify the subject and main verb. Then test how each opening connects the words about isotope patterns and caves to the rest of the sentence.
Step-by-step
Find the verb and match the pair
Step 1Find the method's main verb
Read past the blank to reduces the chance, which says what Velez's method does. The choices change punctuation and verb form, so we need to check both. What is the subject, the thing this sentence is about? It's Velez's method, and its main verb, reduces, already comes after the blank.
- Step 2
Check what compares would add
Would compares describe the method without adding another main verb? Both Velez's method compares and Velez's method, compares make compares a main verb for the method. At location, reduces the chance, another main verb follows with no joining word such as and. Nothing joins the method's compares and reduces.
- Step 3
Test of comparing against the comma
What about Velez's method of comparing? Here, of comparing connects the long description directly to method, making all those words part of the subject. The single comma in any one location, reduces would then separate that subject from its main verb, which isn't allowed. Try crossing out the words about the patterns and caves: you're left with Velez's method, reduces .... That comma isn't closing any extra information.
- Step 4
Open and close the description
Can the description be extra information we can cross out? Comparing is an -ing form that can't be a main verb on its own, so it describes how the method works. The words about isotope patterns from formations in several caves continue through any one location and can be removed with their punctuation, leaving Velez's method reduces the chance ..., a full sentence. The existing closing comma needs an opening comma, so Velez's method, comparing gives the matching pair. Choice B.