After two years' research，we now have a ________ better understanding of the disease.(2013·全国Ⅱ)

I often thought of my childhood,             I lived on a farm.

I felt ______ tired, but he didn’t stop ______.

Chemical pollution will bring about a threat to agriculture and food chain, and ________ to human health.

A society cannot be successful if it throws tradition away, but it cannot be successful ____if we do something to stop progress.