OFFICIAL EXPLANATION
When driving in a residential zone, one must be aware at all times of pedestrians as well as their driving speed.A. pedestrians as well as their driving speed
This answer choice is grammatically incorrect: the pronoun their refers to one but does not agree with it as one is singular and their is plural.
The pronoun one agrees with itself only.
What helps us identify this question as a Pronoun question as well as identify the mistake is the following Stop Sign:
Every pronoun in the underlined part of the sentence or after it
Apart from this grammatical error, this sentence contains a stylistic flaw. Using as well as instead of and is redundant.
What helps us identify this mistake is the following Stop Sign:
B. pedestrians as well as one's driving speed
Although this answer choice corrects the original Pronoun error by using the Pronoun one's instead of their, it repeats the stylistic one. Using as well as instead of and is redundant.
What helps us identify this mistake is the following Stop Sign:
C. one's driving speed as well as pedestrians
Although this answer choice corrects the original grammatical error by using the Pronoun one's instead of their, it repeats the stylistic one. Using as well as instead of and is redundant.
What helps us identify this mistake is the following Stop Sign:
D. pedestrians and of his driving speed
This answer choice corrects the stylistic flaw in the original sentence by replacing as well as with and, but repeats the grammatical one: the pronoun his refers to one but does not agree with it as one is not gender specific while his is masculine.
The pronoun one agrees with itself only.
What helps us identify this question as a Pronoun question as well as identify the mistake is the following Stop Sign:
Every pronoun in the underlined part of the sentence or after it
E. pedestrians and of one's driving speed
This answer choice corrects the grammatical error by using the Pronoun one's instead of their (incorrect pronoun use) and the stylistic flaw (the redundant phrase as well as).