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修改以下句子,选出正确的句子。 To understand the subject, a great deal of studying must be done.
A.
If you want to understand the subject, a great deal of studying must be done.
B.
A great deal of studying must be done t o understand the subject,
C.
To understand the subject, one must do a great deal of studying.
D.
To understand the subject, and a great deal of studying must be done.