Too many factories dispose their waste by pumping it into rivers and the sea.

Đáp án B.

- to dispose of sth = to get rid of sth: vứt bỏ (rác thải). 

Ex: an incinerator built to dispose of toxic waste: lò đốt rác chế tạo để xử lí rác thải độc hại.

- waste (n): đổ thừa, đổ thải.

Ex: household/ industrial waste.

- pump (v): bơm ra, thải.

Ex: The fire department is still pumping floodwater out of the cellars.