At eight o'clock she laid （） whatever she was doing to tell the children a story before they went to bed.

A．away

B．off

C．aside

D．out of

A．条件(1)充分，但条件(2)不充分．
B．条件(2)充分，但条件(1)不充分．
C．条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D．条件(1)充分，条件(2)也充分．
E．条件(1)和(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．

两直线y=x+1，y=ax+7与x轴所围成区域的面积

是