On Call

call on call on On Call call on , call for, call in ,call up 分别是什么意思? 请问on call call on 什么意思 用call on造句 用call on 造句 用call on 与 call at 如何区分call up 和call on call on与call at 的区别 call at a call on sb. call on,call in,call off的区别 call up; call in; call on;分别是什意思 call at造句子1.call at2.call on call at,call out,call on,call up,call off,最好能举例说明一下,. take piace take the place of call at call off call out call on call up call on和 visit有什么区别?call on customers