Sentence Correction - Subject Verb agreement

[ng2]

A risk corridor is one of the main provisions, albeit not the only one, that protects the insurance industry from hitting rock bottom, like it did earlier in the decade.
A. protects the insurance industry from hitting rock bottom, like it did
B. protect the insurance industry from hitting rock bottom, as it did
C. protects the insurance industry from hitting rock bottom, as it did
D. protect the insurance industry from hitting rock bottom, like
E. protect the insurance industry from hitting rock bottom, like they did

OA : B

My question is Should it not have been protects over here since the subject a risk corridor is singular?

[Ali Tariq]

A risk corridor is one of the main provisions, albeit not the only one, that protects the insurance industry from hitting rock bottom, like it did earlier in the decade.
A. protects the insurance industry from hitting rock bottom, like it did
B. protect the insurance industry from hitting rock bottom, as it did
C. protects the insurance industry from hitting rock bottom, as it did
D. protect the insurance industry from hitting rock bottom, like
E. protect the insurance industry from hitting rock bottom, like they did

OA : B

My question is Should it not have been protects over here since the subject a risk corridor is singular?

No.
A risk corridor is one of the main provisions that protect the insurance industry
A risk corrridor is singular.
is is singular.

One of the Xs that/who requires plural verb.
protect is a plural verb.