Owing to the open ---door policy,great changes have taken place since 1978.

问题描述:

Owing to the open ---door policy,great changes have taken place since 1978.

由于有了(正是由于)对外开放的政策,从1978年以来(我国)发生了巨大的变化.
Owing to :由于.
open ---door policy:对外开放的政策
take place:发生(固定短语)