1.happen , take place二者都有“发生”的意思。
happen指事情的发生，往往带有"偶然"的意思。It happens that I am free today. 恰好今天我没有事。take place指事先安排或策划好而后发生，没有"偶然"的意思。
2. must, have tomust表示说话人的主观看法;而have to则表示客观需要。mustn't意为“不可以;不允许”;don't have to意为“不必”。如：(1)My father had to work when he was ten years old。
（2）The play is not interesting. I really must go now。
3. arrive , reach , get to三者都有“到达”之意。reach为及物动词。They reached Tianjin yesterday.昨天他们到达天津。arrive为不及物动词，后面接介词in或at。get to常用于口语，可代替前二者。
4.because , because of二者均表示“因为”because是连词，引导状语从句。We stayed at home because it rained.因为下雨，我们呆在家。because of是短语介词，后面接名词性词语。We stayed at home because of the rain .因为下雨，我们呆在家。
5. in front of, in the front ofin front of…意思是"在……前面"，指甲物在乙物之前，两者互不包括;其反义词是behind(在……的后面)。如：He walked in front of me。他走在我的前面。There are some flowers in front of the house。房子前面有些花卉。in the front of 意思是"在某一空间内的前部"，即甲物在乙物的范围之内;其反义词是at the back of…(在……范围内的后部)。如：There is a big desk and a blackboard in the fount of our classroom。我们的教室前边有一张大桌子和一块黑板。
6. look , see , watch 三者都有“看”的意思。look是看的过程。I looked , but saw nothing . 我看了，但什么也没看见。see是看的结果。see a film看电影see a play看戏(话剧)watch是看移动的事物或定晴地看。watch a football match看足球比赛。watch TV看电视7. sometime; sometimes; some time; some timessometime是副词，可与过去时或将来时连用，表示"(在过去)某个时候"或"(在将来)某个时候"。如： I saw him sometime in May。some time多数情况下作名词短语，意为"一些时间;一些时候";它还可以作副词词组，用来表示一个未肯定的时刻，此时它可与sometime互换。如： I'll be away for some time。sometimes是一个表示时间频率的副词，意为"有时候"。如：Sometimes I help my mother with the housework。some times是"几次、几倍"之意。如：They have been there several times。8. how long, how often, how far, how soonhow long意为"多久、多长时间"，主要是对一段时间进行提问，答语通常是(for)three days/weeks/months等时间段，它可用于各种时态。How long do you stay in Beijing every year?每年你在北京住多久?how often意为"多久……次、是否经常"，用来提问在某一特定的时间进行某个动作的次数，答语通常是always，usually，often，sometimes，once/twice a day/month等。How often do you get to school very early?你多久早到校一次?how far意为"多远"，对距离提问时用。How far is that? 那有多远?how soon意为"还要多久"，是对从某个基本时间到将来某动作结束或某动作发生这段时间提问，常用在一般将来时态的句子中，其答语通常是"in + 一段时间"。-How soon can you finish the work? 还要多久你能完成这项工作?-In half an hour. 半小时后。
