JD.com is one of ________ shopping websites in China.

What caused the accident and who was responsible for it ________ a mystery.[ ]

I often laugh when I see my grandma learning pop songs .But she says,“ One is never ___old to learn.”

Dad, please tell me when Mum _____.I miss her very much.—She will return when she _____her task. And she will bring a nice present for you.

People are bombarded (轰炸) with information________magazines and TV advertising.[ ]