微生物之间的互利共栖关系
参考答案：
微生物之间的互利共栖关系是指在同一个环境中两个微生物类群共栖时，双方在营养提供或环境条件方面都得益的关系。
A man with a big camera in his hands stopped me and asked, “Excuse me! Is there a post office around ______ I can have these posters sent to my friends?”
A．that
B．which
C．where
D．what
高速船救生设备训练手册规定，每周试验通用紧急警报。
