人体中红细胞的直径约为0.0000077m,将数0.0000077用科学记数法表示为( )
A:77×10﹣5
B:0.77×10﹣7
C:7.7×10﹣6
D:7.7×10﹣7
My parents asked me ______ my sister with her schoolwork.
用原文语句回答。