"a" is better here. You don't need "to us" at the end (you've already said "us").

There are three main factors that cause cancer in teens . -- Missing period. Except in casual writing, it's better style to write out small numbers in full. I would personally write "teenagers" rather than "teens".

He's willing to meet any of them/ any one of them. BOTH ARE RIGHT HERE -- Yes. If the cab gets here now, we won't have had much time to talk. Until when is he gone? -- Not very natural. You can say "How long will he be

He had sagged his pants so much, they were dropped to his knees. -- Superfluous space before the comma. This transitive use of "sag" is a little unusual. He's willing to meet any of them/ any one of them. I've lost my

It doesn't sound natural to me. Do you mean "He never talks about family matters."?

It's a strange image. The car appears to grow around you. As it grows, it seems like or becomes like a fairground ride. Pictures of fairground rides: http://images.google.co.uk/images?q=fairground%20ride

There's not really any difference. I suppose "like" is slightly more common in conversation than "enjoy", but "enjoy" is absolutely fine.

"My neighbor says there will be no apple this year. He is very passionate." -- I don't understand what you mean by "no apple this year". What is the context of this statement? "My neighbor , who is very

I am going on holiday for ten days. #3 and #4 are both possible. #4 seems more usual.

When applied to someone engaged in the wholesale buying and selling of physical goods, there isn't much of a difference to me. However, "trader" is also applied to people who buy and sell financial products (such as shares) and