It’s difficult ______ your sound because the noise is too high.

1. A.
   to listen　
2. B.
   to know　
3. C.
   to learn
4. D.
   to hear

 It’s difficult _____ your sound because the noise is too high.

A. to listen　  B. to know　   C. to learn     D. to hear

It’s difficult _____ your sound because the noise is too high.

It’s difficult _____ your sound because the noise is too high.

A．to listen　         B．to know　         C．to learn           D．to hear