4. People begin to know that most environmental problems exist because necessary measures for preventing them _______taken in the past.
—Tom,did you break the vase I bought yesterday?—It was not my .The floor was so slippery that I fell down and knocked it off the table.
I got home,I found I had left my jacket on the playground.
The sooner we students the new school life,the better it will be for our studies.
I must your promise you won’t be late again.
He divided the sweets the children who were divided three groups.