你记住这个就可以,lack既可以是动词,也可以是名词.
动词时,为及物的,所以直接加名词,就是 lack+ sth...就是缺乏什么什么.
They lack money.
名词时,一般用这个词组 a lack of sth.意思也是缺什么.
eg.There is a lack of water in that city.
lacking 是一个形容词,用法为 lacking in sth..
既然是形容词,就是需要它前面加系动词才可以用,或者直接用一个短语.
eg. He got refused because of being lacking in experience.
同一个意思的句子用这三个形式我在给你举个例子：
他缺乏经验.
He lacks experience.
He has a lack of experience.
He is lacking in experience.