ta có tam giác acb đồng dạng với tam giác abd (g.g)

suy ra ab/ac=ad/ab từ đó tính ad=1cm(do có ab=2cm, ac=4cm)

ta lại có tam giác aed đồng dạng tam giác ahb (g.g)

suy ra Sahb/Saed=(ab/ad)^2=(2/1)^2=4=>dpcm

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrases that best fits each of the numbered blanks.

            Kindergarten is a fun place (31)________ young children learn. In some special kindergartens, children learn outside most of the day!

Some kindergartens are (32)________ the forest. In these "forest kindergartens," children play freely. They're outside in all kinds of weather. At forest kindergartens, children learn by climbing trees and picking fruit. They also learn about and (33)________ animals. For example, they collect chicken eggs and feed baby mice.
          Little Flower Kindergarten is in Dong Nai, Vietnam. At this school, children learn about farming. They also learn that it is important (34)________ healthy food. They grow vegetables in gardens - on the roof! They eat the vegetables they grow in their lunches.
At Fuji Kindergarten in Tokyo, Japan, trees grow inside the building! The classroom windows and sliding doors (35)________ open to the outside most of the year. The roof is a big, wooden circle. Children love to play and run on it.

Điền vào số (31)

A. why     

B. when      

C. where     

D. which

Sarah: “What time shall we leave?”                Tom: “__________ .”

A. Soonest and best.                                      

B. The soonest and the best.

C. As soon as good.                                      

D. The sooner the better.