消化系统功能减退、向心性肥胖、糖耐量降低、衰老、易感染（）
A.胎儿期
B.婴幼期
C.学龄期
D.青少年期
E.老年期
参考答案：E
High-speed trains travel at 300 kilometers an hour，which is about normal trains．
A．four times the speed as
B．the speed four times of
C．four times as the speed of
D．four times the speed of
RS232-RS485通讯转换器的传输距离要求与连线方式是什么？
