Air pollution is getting more and more serious，so we must take action________it is too late

I greeted the teacher with “ hello”, and the teacher gave me a sweet smile ______

to the Internet, large quantities ofinformation are now _____ to us in our home

I don’t think he could have done such a stupid thing last night, ______? [ ]

(2013·浙江温州二模)Scientists have found evidence ________ global warming caused the world’s first horses to become smaller nearly 50 million years ago.