呼吸作用的实质是：　　　　　　　　　　　　　　　　　　　　　　　（　 　）

Fill in the blanks with the proper forms of given words.

I helped my mother to buy some beef and three____ (potato) for supper today.

"Belt and Road"（一带一路) are the two wings of developing Asia in the____ (twenty-one) century.

Please keep____ (silence) in the concert hall because people are enjoying Lang Lang's piano performance.

Candy ____ (lay) out the tea, fruit and snacks on the table and waited for the visitors.

.With the development of technology, mobile phones are ____ (wide) used these days.