关于血细胞计数误差来源，不属于偶然的误差的是
A．取血部位不当
B．稀释倍数不准确
C．充液不当
D．计数板刻度误差
E．计数时未充分混匀
参考答案：D
Playing basketball is sometimes very tiring, ______ I enjoy it very much.
A．so
B．but
C．if
D．or
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