Determine the verb for the first gap.

The first gap is part of the relative clause "who .... in the premises". The relative pronoun "who" refers to "ladies". Since "ladies" is plural, the verb that follows "who" must also be plural.

• "sells" is a singular verb.
• "sell" is a plural verb. Therefore, the first gap should be "sell". This eliminates options A and C.

The second gap is the main verb of the sentence. The main subject of the sentence is "One" (from "One of the ladies"). "One" is a singular subject. The verb must agree with "One".

• "have" is a plural verb.
• "has" is a singular verb. Therefore, the second gap should be "has".

The first gap is "sell" and the second gap is "has". This matches option D.

The complete sentence is: "One of the ladies who sell in the premises has been asked to withdraw."

The correct option is D.

The answer is $\boxed{\text{D. sell/has}}$.