Question 31·200 Super-Hard SAT Reading Questions·Standard English Conventions
Scientists have long sought ways to curb frost damage in vulnerable plants. Recently, plant pathologist Dr. Mei Liao analyzed a new strain of the bacterium ______ and discovered that it produces far fewer ice-nucleating proteins than typical strains.
Which choice completes the text so that it conforms to the conventions of Standard English?
For SAT punctuation and boundary questions, first strip the sentence down to its core: identify the subject and the main verbs, and check whether and is joining two whole clauses or just two verbs (a compound predicate). Do not place a comma between one subject and its two verbs. Next, look at descriptive or naming phrases and decide if they are essential to identify the noun; if they are essential, they should not be set off by commas, and you should not insert commas between a verb like called and the word or phrase that completes its meaning. Use these rules to eliminate choices that create unnecessary pauses or break up the main grammatical units of the sentence.
Hints
Locate the subject and verbs
Ignore the blank for a moment and read around it: who is doing the actions, and what are the two actions that person takes?
Think about the comma before “and discovered”
Ask yourself: when one subject does two things in a row (verb1 and verb2), do we usually put a comma before and? Look at which answer choices would create a comma right before the word and.
Decide if the name is essential or extra
The phrase that gives the strain’s name is part of the noun phrase. Is that name necessary to identify which strain Dr. Liao analyzed, or is it extra information that could be removed without changing the main meaning? That will tell you whether to use commas around or inside that phrase.
Step-by-step Explanation
Understand the structure of the sentence
Focus on the key part of the sentence: plant pathologist Dr. Mei Liao analyzed a new strain of the bacterium ______ and discovered that it produces far fewer ice-nucleating proteins than typical strains.
Here, the subject is Dr. Mei Liao. She does two actions: she analyzed a new strain and discovered something about it. Those two verbs, analyzed and discovered, share the same subject and form a compound predicate (two verbs for the same subject).
Apply the rule for commas with a compound predicate
When one subject has two verbs (a compound predicate), we normally do not put a comma before and between those verbs.
So we do not want a comma right before the words and discovered. Any choice that makes the sentence read like ...bacterium [blank], and discovered... incorrectly places a comma in the middle of the compound predicate and should be eliminated.
Decide how to punctuate the naming phrase
The blank must give the specific name of the strain: it is a strain of the bacterium that is called CLX3. That naming phrase is essential to identify which strain is meant, so it should not be set off by commas or broken up by a comma between called and CLX3.
The only option that (1) avoids a comma before and discovered and (2) keeps the essential naming phrase together without any internal commas is “called CLX3”, which is therefore the correct answer.