在G+和G-细菌细胞壁的肽聚糖结构中，甘氨酸五肽是其肽桥的常见种类。（）
参考答案：错
The government has taken a series of measures to _________ people’s needs in our country, which has provided good opportunities for many companies.
A．explain
B．expand
C．export
D．expect
switch语句中( )。
A．必须有default子句
B．不必有default子句
C．必须有default子句和至少有一个case子句
D．必须有default子句，不必有case子句
