没有动词变y为i加ing的情况，
相反：以ie结尾的要变成y再加ing.如：
lie-lying
tie-tying
动词ing变化规则
动词ing变化规则如下：
一、特殊的需要变化形式：
1、以不发音的e结尾，去e+ing.
例如： skate的动词ing形式为skating;hope的动词ing形式为hoping；write的动词ing形式为writing.
2、以ie结尾，去ie变y+ing.
例如：die的动词ing形式为dying；lie的动词ing形式为lying；tie的动词ing形式为tying.
3、以重读闭音节结尾，末尾只有一个辅音字母的动词，双写辅音字母+ing
例如：get的动词ing形式为getting;begin的动词ing形式为beginning；swim的动词ing形式为swimming；run的动词ing形式为running.
二、不需要变化形式：
动词后直接+ing(这种是最常见的)
例如：Read的动词ing形式为reading;go的动词ing形式为going.
动词不定式用法
动词不定式在句中可充当主语、表语、宾语。
一、作主语
动词不定式作主语可位于句首。例如：
To learn a skill is very important for everyone in society.
也可使用it作形式主语，而将其置于句末。例如：
It is necessary for young students to learn a foreign language.
二、作表语
动词不定式作表语常用于以下结构：My wish/ job/ aim/ goal is…及The next step/ measure is …等。例如：
Your job is to type the papers in the office.
The next measure is to stop the river from being polluted.
三、作宾语
常见的只能使用动词不定式作宾语的动词有：agree, choose, decide, hope, fail, wish, refuse, expect, manage, plan, intend, pretend, promise, offer, afford, demand, arrange等。 例如：They decided to build a highway between these two cities.
She offered to help me when I was in trouble.
believe, think, consider, feel, make等动词可用于“动词+ it +adj./ n+to do sth.”句型，其中使用it作形式宾语，而将真正的宾语动词不定式置于句末。例如：
I think it necessary for us to have a good rest after the long work.
She felt it her duty to help the old woman.
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