Writing: Identifying Sentence Errors

The following sentence contains either a single error or no error at all. If the sentence contains an error, select the one underlined part that must be changed to make the sentence correct. If the sentence contains no error, select choice E. 
Identifying Sentence Errors questions are fairly self-explanatory. Four sections of the sentence are each marked with a letter, and you need to read the sentence and identify the error. If there is no error, then "No Error" is the correct answer. Write the letter of your choice in the margin and you're done! (Gridding a whole page at the same time is more efficient than gridding one answer at a time, so as you finish each question you should write the answer in the margin.)
The new law requires that all bicycle riders have been wearing helmets while on their bicycles, even when they are not moving. No error.
The Knowsys Method is all about predictions, so I have temporarily removed the answer choices from the sentence. Read it to yourself, silently or aloud. Does anything sound strange or wrong? Does anything seem illogical? 

In fact, the law according to the current sentence mandates something not just illogical, but impossible.

The new law requires that all bicycle riders have been wearing helmets...

"Have been wearing" is past tense (past perfect, to be precise), so the law apparently requires that bikers, in the past, were wearing helmets. Since it is impossible to comply with a law that has not been written, and since it is illegal to prosecute someone for a "crime" committed before the act was illegal, this sentence is nonsense.  Now, look at the answer choices:

The new law requires that all bicycle riders have been wearing helmets while on their bicycleseven when they are not moving. No error

Sure enough, the verb phrase "have been wearing" is underlined. A is the answer. However, it is important to check the grammar of the other answer choices to ensure that you selected the best answer.

B) "While" is a subordinating conjunction that tells when the bicycle riders must wear their helmets.
C) "Their bicycles" is correct because the possessive pronoun "their" matches both its antecedent "bicycle riders" and the noun "bicycles" it modifies. Remember that possessive pronouns, like possessive nouns ("Jimmy's") act like adjectives and must modify nouns. An antecedent is the noun that a pronoun replaces.
D) "Even when" is correct. "When" is a subordinating conjunction like "while," and "even" is an intensifier that emphasizes the subordinate clause "when they are not moving."

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