21. It is a good idea to __________ our clothes with our friends or cousins.

           A. Change              B. Swap          C. Turn          D. Send

⇒ swap: tráo đổi

22. If people turn off all electric appliances in one hour all over the world, they can save a lots of __________ .

           A. Electric               B. Electrical          C. Electrician           D. electricity

⇒ electricity: điện

⇒ a lot of + N

23. You should put the food in a reusable box __________ plastic bags. 

          A. By                        B. Instead of        C.Because of           D.Without

24. If we use __________ paper, we will save a lot of trees. 

          A. Fewer                 B. Less           C. More           D.Much

⇒ instead of: thay vì

25. Don’t throw rubbish into the river because you will make it __________. 

         A. Greener               B. Dirty          C. Cleaner        D. Fresher

⇒ dirty: bẩn thỉu

26. If there is a rubbish bin in every class, the classroom will become______ 

        A. Harmful               B. Lighter       C. Dirtier           D. Cleaner

27. If we all use__________ bags, we will help the environment. 

        A. New                     B. Cheap       C. Reusable       D. Reduced

$\text{21.}$ B

$\text{→}$ swap: tráo đổi

$\text{22.}$ D

$\text{→}$ electricity: điện

$\text{→}$ a lot of + N

$\text{23.}$ B

$\text{→}$ instead of: thay vì

$\text{24.}$ B

$\text{→}$ paper ko đếm dk dùng less

$\text{→}$ fewer + N đếm dk

$\text{25.}$ B

$\text{→}$ dirty: bẩn thỉu

$\text{26.}$ D

$\text{27.}$ C

$\text{→}$ reusable: có thể tái sử dụng