求由曲线y=ex，y=e-x及x=1所围成的平面图形的面积以及此平面图形绕x轴旋转一周所成的旋转体的体积Vx.
We sent the letter by airmail （以便他们能及时收到）.
The government official said that the new tax rates would come into ______ (effective) from April.
We will agree to sign the new contract provided that you increase our salaries by 5%.
His______(refuse) to come to our wedding upset the new couple.
