Flash中帧的类型不包括（）。 A.中间帧 B.帧 C.空白关键帧 D.关键帧

Thinking of the days, when he was looked down upon as a poor peasant, _______.[ ]

A. his heart was filled with sorrow      

B. tears came down his face

C. he was in great sorrow            

D. we found him wiping his eyes

毛囊下端膨大成球的部分是（）。

A.毛 * *

B.毛基质

C.毛球

D.毛根

( )是人民警察的象征与标志。

A．警歌
B．警纪
C．警徽
D．警服

简述柑橘罐头出现白色沉淀的原因及预防措施。