At times the balance in nature is ______，resulting in a number of possibly unforeseen effects.

I like this jacket better than that one, but it costs almost three times _______.

--- What has become of the spaceship?-- It landed ______.

We'll be away for two weeks because we'll have a ___________.

The　president　made　a＿＿speech　at　the　opening　ceremony　of　the　sports　meeting，which　encouraged　the　sportsmen　greatly．