可唔可以幫我人手check grammer?? thanks..

A root cause describes the source of a problem. Unless you have scientific proof that pressure causes people to smoke and most of the smokers smoke because of pressure, using "root cause" would be inappropriate here.

People have, face, or experience pressure; they don't usually suffer from pressure.

In the second sentence, you indicate that misconception is one of the main reasons. This totally disproves your first sentence because there is not one root cause for smoking. What misconception do people have? You need to give examples to prove your point.

The third sentence is generally fine, although it goes back to the idea of pressure again. It should then be combined with the first sentence.

The last sentence is also problematic. People who smoke are not smoking people :) We usually call them "smokers."

Overall, the organization is weak. You should first define the purpose of your passage (What subject matter are you trying to address?), then come up with your position and your points (What you do think about the subject? Why do you think so? What are the reasons that support your thoughts?), and organize your ideas into a cohesive presentation.

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Here is a revision based on your ideas:

The main cause of the acute smoking problem in Hong Kong is the pressure faced by many people. They believe that smoking can relieve their stress from interpersonal relationship and work. In addition, some folks, especially the young, have misconceptions towards smoking, thinking that smokers are cool and mature. This leads more teenagers into smoking.

The root cause for acute smoking problems in Hong Kong stem from the great pressure suffer by Hong Kong people
One of the many misconception people have towards smoking, especially within youngsters is that they often considers smoking as something that helps them to alleviate pressure cause by work and interpersonal relationship.
Also some are even so naive to label people who smoke as cool and mature.
Therefore, smoking has become a bad trend amongst some groups of teenagers.

the root cause你是不是想說最底層的原因
我覺得-The main reason of acute 會好一點

great pressure suffered 可以說成 the stressor going around and around every HK people
意思係D壓力一真包圍著每一個香港人

futhermore, many misconception towards smoking by people, expectially the youngsters,beside these,People often considered that smoking can help alleviating pressure from interpersonal relationship and works.

Some people are even naive to label smoking people as [cool] and [mature].
Therefore, smoking become a bad trend among some groups of teenager.