60.  A from time to time   B  in time    C  sooner or later   D on occasion

Personnel working aloft (above 2metres) should wear（）or other arresting device at all times.

It should be apparent that little or nothing is gained by opening a drain at the same time as or after admitting steamThe above sentence probably means （）.

Project（71）is an uncertain event or condition that，if it occurs，has a positive or a negative effect on at least one project objective，such as time，cost，scope，or quality．

Project ______is an uncertain event or condition that，if it occurs，has a positive or a negative effect on at least one project objective，such as time，cost，scope，or quality．

● Project（71）is an uncertain event or condition that, if it occurs, has a positive or a negative effect on at least one project objective, such as time, cost, scope, or quality.（71）

I remembered the day when World War II finished I was eight or nine at the time , and we heard it ___ when we were at the table

I remembered the day when World War II finished I was eight or nine at the time , and we heard it ___ when we were at the table

Jitter is an unwanted variation of one or more characteristics of a periodic signal in electronics and telecommunications and（）refers to call issues that cause variations in timing or time of arrival.

At that time we thought the story ______ not be true.

“挑战杯”全国大学生竞赛包括哪两类赛事（）

哈工程学生近3年在“挑战杯”中国大学生创业计划竞赛及课外学术科技作品竞赛、亚太及全国大学生机器人电视大赛、美国国际大学生数学建模竞赛、全国大学生电子设计竞赛等各类国际国内赛事中获得国际、国家级奖（）余项。