原句：
It is easy to make out the twins because they have difference hairstyle.
改正：It is easy to make out the twins because they have a difference hairstyle.
解释：在"difference"前添加冠词"a"，因为"hairstyle"是可数名词，需要冠词来修饰。
原句：
Mary tried to catch Tom's eye by dressing in strange costume.
改正：Mary tried to catch Tom's eye by dressing in a strange costume.
解释：在"strange"前添加冠词"a"，因为"costume"是可数名词，需要冠词来修饰。
原句：
I apologize on behalf of Tom to her for not going to her party.
改正：I apologize on behalf of Tom to her for not going to her party.
解释：此句没有语法错误，但为了清晰起见，可以稍微调整一下标点符号。
原句：
Each of them are hard-working.
改正：Each of them is hard-working.
解释：因为"each"是第三人称单数，所以动词"are"应改为"is"。
原句：
We'll never forget the days when we spent together in the mountain village.
改正：We'll never forget the days we spent together in the mountain village.
解释：去掉"when"，因为"the days"已经作为先行词，不需要"when"来引导定语从句。
原句：
Do you still remember the village where we paid a visit to last summer？
改正：Do you still remember the village where we paid a visit last summer？
解释：去掉"to"，因为"pay a visit"是一个及物动词短语，不需要加"to"。
原句：
This is the best hotel.
改正：This is the best hotel.
解释：此句没有语法错误，但为了清晰起见，可以稍微调整一下标点符号。
原句：
I have been to Fun Times last week.
改正：I went to Fun Times last week.
解释：将"have been"改为"went"，因为"last week"是一般过去时的时间标志，所以谓语动词要用过去式。