10點 請熟知國中英文文法的大師相助

Some people think riding motorcycle is dangerous.
=>
It is thought by some people that riding motorcycle is dangerous .

It is dangerous to ride a motorcycle, so to be thought by some people.
Some people think =某些不確定人士的想法=聽說=據說=they say
They say that it is dangerous to ride a motorcycle.(真理,say用現在式）
It is dangerous to ride a motorcycle, they say.
如果你確知某一群人的某些人已經說過這句話,則可用直接語氣這麼寫：
Some people said,"It is dangerous to ride a motorcycle."
或：
"It is dangerous to ride a motorcycle." said some people.（過去動作,said用過去式.

It is in some people's mind that riding motorcycle is dangerous.

It is said....?

It is dangerous for riding motorcycle by some people think.