Although the causes of cancer_____, we do not yet have any practical way to prevent it.
A．a(chǎn)re being uncoveredB．have been uncoveringC．a(chǎn)re uncoveringD．have uncovered
A
因?yàn)榫渥拥闹髡Zthe causes of cancer與謂語uncover 是被動關(guān)系，因此我們使用被動結(jié)構(gòu)，只有A 符合這一條件。
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