After visiting different countries, I found _______ very important to learn about table manners.

A. it                B. that            C. this              D. us

I find _______ difficult to finish the work on time. We only have three hours left.

A.it                               B. that                     C. its                             D. this

－ I need something for cutting the paper.

     － Oh, you want a knife? OK, I'll get ______ for you.

A. it                    B. that                      C. this                        D. one

________is dangerous for us to swim in the river alone.

A. It                   B. That                   C. This