for a certain time一定量的时间,可是time是不可数名词,为什么会有个"a"

for a certain time一定量的时间,可是time是不可数名词,为什么会有个a offers you a chance to live with a new family for a certain time for certain reason还是for a certain reason 区别几个与'time有关的词组at certain time at certain timesat a certain time 这些词组都对的吗?有什么区别呢? Sometimes really miss a certain period of time.... at some certain time a certain we have reached a certain respect for each other Your experience of entering for a certain kind of competition . are you certain ____ the facts? A about B for know for certain是什么意思? 英语翻译By means of the “recording window” functions a certain storage time interval for active data acquisition can be selected,allowing the suppression of unwanted recording,if a long pre-(or post-)treatment time is desired. for a time造句! a time for time for a quiz 用括号里适当形式填空 they (certain)had aig time at the culb last nightthey (certain)had a big time at the club last night 问一道托福题Paragraph5:Scientists have known for some time that certain plants,calledhyperaccumulators,can concentrate minerals at levels a hundredfold or greater than normal.■ A survey of known hyperaccumulators identified that 7 5 percent o 请高人帮我翻译一下这句话,百度、谷歌翻译勿扰!Note the difference between features and benefits, and think about them. For example, a house that gives shelter and lasts a long time is made with certain materials and to a certain de