While every possible means __________ to prevent the river pollution, the river in my hometown has still not been restored to its past beauty.
A.is tried | B.are tried |
C.has been tried | D.have been tried |
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While every possible means __________ to prevent the river pollution, the river in my hometown has still not been restored to its past beauty.
A.is tried | B.are tried |
C.has been tried | D.have been tried |