六淫是指（）
A.六气
B.六气不及
C.六种毒气
D.六种外感病邪的统称
E.风、寒、暑、湿、燥、火
参考答案：D
He started to learn English in 1990 and in the years ________ he kept on using it in his work.
A．following
B．followed
C．follow
D．that followed
现代物流系统需要具备哪些主要特点
