summer decides to sneak into the museum by pretending to be: merchants students sightseers guides

Brief Explanations:

There is no additional context given, but students are often in groups and might be less - scrutinized when entering a museum compared to the other options. Merchants are not a typical group to enter a museum in a sneaky way, sightseers are usually expected to enter normally, and guides are usually known to the museum staff.

Answer:

B. students