设函数f(x)=ax3＋bx2＋cx＋d，问常数a，b，c满足什么关系时，f(x)分别没 有极值、可能有一个极值、可能有两个极值?

曲线y=x3-3x+2的拐点是__________。

He developed computer software to handle complicated______(finance) transactions.

His______(refuse) to come to our wedding upset the new couple.

We will agree to sign the new contract provided that you increase our salaries by 5%.

The government official said that the new tax rates would come into ______ (effective) from April.