It's和This is的区别?

dress有不同解释：动词.
1.给...穿衣;打扮;替...做衣服
The mother is dressing her baby.
母亲正为婴孩穿衣.
2.使穿着[H][W]
She is dressed in black today.
今天她穿一身黑.
3.给(伤口)敷药;包扎
The nurse dressed his wound.
护士替他包扎伤口.
4.调制(色拉);制作(菜)
She dressed the vegetables with butter and salt.
她在蔬菜里面加上黄油和盐.
5.梳理(头发);装饰(橱窗等)
He was dressing the shop window.
他在布置商店橱窗.
6.整(队)
vi.
1.穿衣;打扮
The girl dresses fashionably.
那女孩穿着时髦.
2.穿晚礼服
She is dressing for the party.
她在穿礼服准备去参加晚会.
3.整队
n.
1.女装;连衣裙[C]
All the pretty women wore their smartest dresses.
所有漂亮的女士都穿着最漂亮的连衫裙.
2.衣服;(特定的)服装(如民族服装,礼服等)[U]
Few people wore evening dress.
几乎没有人穿晚礼服.
这道题旨在于问你it's 作代词和物主代词的用法.没什么区别,翻译过来都是这是我儿子的,是他的!或者它是我儿子的,那是我儿子的.这样用对,dress这里指晚礼服或者是民族服装,或者特定的服装!it's做物主代词来讲能代替很多,可以是人也可以是物（单数）,比如he,she,Mr Hu,son 等等
Whose's this pen?
It's my son's.
This is his pen.
其意思是：这是谁的笔?
那是（它是）我儿子的.
（说话的人手拿那支笔又说）这是我儿子的!