He was playing the guitar at his brother's wedding last night.

• B: "was playing" (past continuous) should be used for an ongoing action in the past.

The bus left the station at 6 a.m. yesterday morning.

• B: "left" (simple past) should be used for a completed action in the past.

She used to ride a bike to school when she was a very young girl.

• D: "was" (simple past) should be used to indicate past habits.

Mr. Quan didn't go to the movies with us yesterday morning because he was sick.

• B: "didn't go" (simple past) should be used instead of "didn't went".

Three years ago, Mr. Hieu played soccer with his children in the yard.

• C: "played" (simple past) should be used for a completed action in the past.

Last week, she wrote two letters to her parents in the countryside.

• B: "wrote" (simple past) should be used instead of "writed".

True (T): Blood donation can save millions of human beings from death.

False (F): A lot of laboratories do not manufacture blood.

True (T): Unavailability of blood may cost lives.

False (F): Blood donation is not harmful; it is considered safe and harmless.

True (T): Today's donor may become tomorrow's recipient.

Volunteering in our communities makes a difference.

We should help the homeless, poor children, and the elderly.

Last week, my class volunteered to clean the streets.

My brother has donated blood three times before.

The lakes are full of rubbish. We should ask our friends to clean them this Sunday.

My dad has been to London, but he did not see Big Ben.