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。mustnt意为“不可以;不允许”;dont 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 , be
