I.                    Put the word in brackets into the correct form.

1.      All the staffs _______________ to wear protective clothing by the health and safety regulations. (require)

2.      There are various _______________ open to someone who is willing to work hard. (opt)

II.                  Rewrite the sentences.

3.      She found singing songs difficult.

è (find) __________________________________________________________________

è (find) __________________________________________________________________

è Singing songs ___________________________________________________________

4.      They used to play sports well.

è ______________________________________________________________________

______________________________________________________________________

cho S=5+5²+5³+...+5²⁰²⁰+5²⁰²¹. Chứng tỏ rằng 4.S+5=5²⁰²²