悠悠文明史，漫漫丝绸路．我国素来以“缫丝养蚕”著称于世．你可知道蚕丝是家蚕发育过程中哪一时期的杰作（ ）
A. boy.
B. It's black.
C. Yes, he is.
D. Her name is Li Hua.
E. She is my English teacher.
