正压式呼吸器的主要用途是什么？
参考答案：
主要用于危险作业、抢险时的个人防护。
改错：从下面的句子中找出错误并改正。
1. What is your mother? She's fine, thank you. ( )___________
A B C D
2. You are a teacher, right? Yes, I'm. ( )___________
3. What is this? It is desk. ( )___________
4. Look! Spotty is under chair. It is eating. ( )___________
何种移动站不需要天线自动跟踪装置（）。
A.Inmarsat-F
B.Inmarsat-B
C.Inmarsat-C
D.Inmarsat-M
