那些动词后用原形动词(infinitive without “to” )? (来源：英语学习门户 http://www.EnglishCN.com)
动词后用原形动词(infinitive without “to”)的有：
behold(12 世纪前用字，现代英文中极少用)，bid, feel, have, hear, let, make,
observe, perceive, see, watch, 另help后，可用to(英式英文)或不用to(美式英文)。
play piano or play the piano？
例如：He plays the organ in the church on Sundays.
She practices playing the violin almost every day.
sometime vs. some time vs. sometimes
1. sometime: (过去的)某一时候；来日，改天
例如：I stayed in Taichung sometime last summer. 去年夏天某个时候，我待过台中。
例如：I’ll go to Taichung to see you sometime next summer. 明年夏天某个时候，我
2. some time: 一段时间
例如：I stayed in Taichung (for) some time last summer. 去年夏天，我在台中待过一段时间。
3. sometimes: 有时候
例如：Sometimes I go to Taichung for business. 有时候我去台中出差。
What a beautiful girl she is! vs. How beautiful a girl she is!
两句都是惊叹句，意思一样，只是一用what, 一用how开始。如用what开始，则是 what a + 形容词；如用how开始，则是how + 形容词。
I have just received a letter from my father
I just received a letter from my father
Just当刚才或方才（a moment ago）解释时，英式英文用现在完成式，美式英文用简单过去式。但just now（刚才）不论英式英文或美式英文均用简单过去式。
例如：I received a letter from him just now.
go to bed vs. go to sleep
go to bed 是就寝，go to sleep是入睡。我们可以确知自己几时、几分、甚致几秒就寝，但却无法确知自己几时、几分入睡。
例如：I always go to bed at 11 o’clock every night.
I don’t know when I went to sleep last night.
ago vs. before
例如：He transferred to another university two years ago. transferred是过去式，是从说这句话时推算two years ago.
He told me that he had transferred to another university two years before.
told是过去式，had transferred是过去里的过去(past in the past)，因为它发生在过去式told之前，此时时态要用过去完成式，并用before, 否则他可能是两年前或三年前告诉(told)我，加两年或三年便是四年或五年了，而非两年前。
此外，在直接句改为间直接句时，如直接句中有 ago，间直接句中要改为 before.
例如：Direct: Joy said, “I read that novel a year ago.”
Indirect: Joy said that she had read that novel a year before.
The house which I went into is big.
The house into which I went is big.
The house which I went into is big. 是一般的英文。
The house into which I went is big. 如将into 放在which之前，即是该句的加强句。
此外亦可写为The house that I went into is big.( 非正式英文。)
但如写为The house into that I went is big.因为that 作关系代名词用时，前面不得用前置词。
形容词子句中关代用 that 时与名词子句如何区分？
1. The fact THAT she has inner grace(内在美) is more important.
2. The fact THAT we must recognize is the lack of respect for the old.
3. I like the student THAT is gentle and respectful.(彬彬有礼)
第一句中THAT是连接词，连接The fact与 she has inner grace.
THAT she has inner grace是名词子句，作the fact的同位语，而且
she has inner grace可独立成句。
在名词子句中的THAT也称为名词子句的符号 (the sign of noun clause)。
That fact WHICH we must recognize is the lack of respect for the old.
第三句中THAT也是关系代名词，作为is gentle and respectful的主词
第二、三句中we must recognize(无受词)及is gentle and respectful(无主词)
摘译自拙著p.134, Practical English Grammar and Rhetoric(实用英文文法与修辞. 第九版第五刷)
on Taiwan vs. in Taiwan
在岛上的「在」用 on英国人用 on但亦可用 in. Taiwan 是一个岛，所以用on 或in.
例如：He lives in (on ) Taiwan.