Mary speaks in a low voice; ____ is difficult to know what she is saying.

1. A.
   it
2. B.
   that
3. C.
   so
4. D.
   she

Mary speaks in a low voice; ____ is difficult to know what she is saying.

A. it            B. that            C. so                  D. she

Mary speaks in a low voice; ____ is difficult to know what she is saying.