烧结空心砖，其特点是：孔洞个数少但洞腔较大，孔洞率大于或等于

搜题请搜索小程序“爱下问搜题”

问题单项选择题

烧结空心砖，其特点是：孔洞个数少但洞腔较大，孔洞率大于或等于( )，孔洞垂直于顶面，平行于侧面。

A．30%
B．20%
C．25%
D．35%

答案

参考答案：D

填空题

1.	This is my ___________. He is 42 years old. He is a ___________.
2.	This is my ___________. She's 40 years old. She is a ___________.
3.	This is my ___________. He is 20 years old. He is ___________. He is a ___________.
4.	This is my ___________. She is 6 years old. She is ___________. She is a ___________.

问答题简答题

简述GSM跳频的意义.