These machines can help recycle the waste which would be thrown away.
A. otherwise
B. therefore
C. however
D. though
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(答案→)A. otherwise
B. therefore
C. however
D. though
解析：考查词义辨析。otherwise 否则，要不然，therefore 因此，however 然而，though 然而，这些机器能帮助回收要不然会扔掉的废物。所以选A。