问题详情

Maximum alertness was normally achieved ______.
A．form. 8-11 a.m. and 9-12 p.m.
B．between 3 p.m. and 5 p. m.
C．form. 9-11 a.m. and 9-11 p.m.
D．between 8-20 a.m. and 7-9 p. m.请帮忙给出正确答案和分析，谢谢！