our earth, or else it will be no longer fit for us to live on.

He lives ______, but he never feels _________.

Elworth’s barn burned down, but they saved what cattle _______ were in the barn.

The following chapters provide step-by-step instructions for practical _______ of genetic (基因)engineering to agriculture.

Mum, I can’t find my football.—Hurry up! Your father ______ for us.