—Do you know the most ancient city in China—Xi’an well?

—No，this is the first time I ________ here. 

A．came

B．have come

C．am coming

D．come

胎儿时期下列哪个系统发育最早（）

A.呼吸

B.循环

C.神经

D.泌尿

E.内分泌