am=3，an=2，求a2m-3n。
解：a2m-3n= a2m÷a3n=（am）2÷（an）3= 32÷。
Most Americans would prefer to keep their problems _____themselves, and solve their problems ______ themselves.
A．to; by
B．by; to
C．for; to
D．in; on
四大文明中哪一个文明与其他三个文明不在同一纬度上呢？（）
A、古埃及
B、中国
C、巴比伦
D、印度
。 
。