Most volunteers are from universities, it is not unmon to see middle and primary school students too.
A. though
B. however
C. since
D. even if
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(答案→)A. though
B. however
C. since
D. even if
解析：句意：尽管普遍可以看到中学生和小学生，但是大多数志愿者来自于大学。Though尽管；however不管怎样；since自从；even if即使，选A。