Although the causes of cancer ________, we do not yet have any practical way to prevent it．
A．have uncoveredB．have been uncovering
C．a(chǎn)re uncoveringD．a(chǎn)re being uncovered
D
考查時(shí)態(tài)語(yǔ)態(tài)，句意是;雖然癌癥的原因正在被揭示出來(lái)，我們還是沒(méi)有實(shí)用的方法來(lái)阻止它，因?yàn)榘┌Y是被揭示，用被動(dòng)式，幾個(gè)選項(xiàng)只有A是現(xiàn)在進(jìn)行時(shí)的被動(dòng)。選D。
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