Answer:
B. An incoming charged tRNA binds to this site.
Explanation:
This is part of a process called TRANSLATION, in which mRNA is translated into proteins by the ribosomes, it comprises 3 stages: Initiation, Elongation, and Termination.
The A site is part of the ribosome, which has 1 binding site for mRNA and 3 binding sites for tRNA: A: Aminoacyl or acceptor site; P: Peptidyl; E: Exit, and it´s involved in ELONGATION, where it binds to the Aminoacyl tRNA (charged tRNA), that has the aminoacid that´s going to be added.