Question

There have been great changes in China s_____ it opened to the outside world thirty years ago.

Answer 1

There have been great changes in China SINCE（填空用大写标出以醒目） it opened to the outside world thirty years ago.
自从30年前改革开放以来，中国产生了巨大的变化。

since：自从什么以来，主句是现在完成时。

绝对准确，望采纳！

Answer 2

呃，楼上那位回答的很准确，望采纳。