Respuesta :
1. If you don't like the blue shirt, you **could** try the grey one.
2. She **could** easily lift weights of 60 kilos when she was young.
3. If I were you, I **should** try the grey one. (Note: "shall" is also grammatically correct, but "should" is more commonly used in this context.)
4. **May** I come in, please?
5. **Must** not leave the campus without informing your teacher.
6. You **can** ask for a refund.
7. In the future, people **will** be communicating. (Note: "can" and "could" are also possible depending on the context, but "will" emphasizes the inevitability of the action.)