A Cambodian boy has become famous on the Internet. When ________ about how he picked up so many languages, he said he learned them from other tourists.

下列句子有语病的一项是（ ）

Not until they left school ____how much their teachers loved them and helped them.

Has he returned from Canada_________— Yes, he’s _________ come back.

Have you known DrJackson for a long time?—Yes, since she _________ the Chinese Society