医师和药学专业技术人员在药物临床应用时须遵循的原则包括（）

A.安全

B.有效

C.经济

D.适当

E.尊重患者的知情权

—I hear Mr. Zhang has gone to Beijing for a meeting.

—Really? Do you know when he ______?[ ]

A. leaves

B. was leaving

C. has left

D. left