Although the causes of cancer_____, we do not yet have any practical way to prevent it.

 A. are being uncovered  B. have been uncovering C. are uncovering  D. have uncovered

Although the causes of cancer ____we do not yet have any practical way to prevent it.

A.     are being uncovered  B. have been uncovering

C. are uncovering   D. have uncovered

 Although the causes of cancer ____, we do not yet have any practical way to prevent it.

A. are being uncovered      B. have been uncovering  

C. are uncovering          D. have uncovered

 Although the causes of cancer_____, we do not yet have any practical way to prevent it.
    A. are being uncovered  B. have been uncovering C. are uncovering  D. have uncovered

Although the causes of cancer_____, we do not yet have any practical way to prevent it.