当总成本曲线的切线通过原点时，SAC（）
A.最小
B.等于SMC
C.等于SAVC加上AFC
D.以上都对
参考答案：D
He is known _____ a scientist and famous _____ his research on rice.
A．for; as
B．for; for
C．as; for
D．as; as
火风压的影响主要在起火房间。（）
