Need help with question

Contrastive sounds in a language are usually not as different from each other in natural settings as they are in carefully controlled experiments. Hitczenko and Feldman's results show that your _________ ability to interpret acoustic differences as either contrastive or noncontrastive may come from the contexts in which they hear different sounds.

Which choice completes the text so that it conforms to the conventions of Standard English?

• A

• infants'

• B

• infant

• C

• infants

• D

• infant's

P.S. This is from a third-party tutoring website. I chose D, the answer choice on their website was A. I asked multiple AI's, some say A, others say D. Thanks!