精品一区二区免费在线观看_国产精品久久久久久av福利软件_97成人精品区在线播放_国内成人精品一区

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.

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

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．have uncovered             B．have been uncovering  

       C．are uncovering        D．are being 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