下列各句中，没有语病的一句是（ ）

last decade, Chicago public schools ________teaching of Chinese to serve 12,000 students.

When speaking in public, it is important to _____ your message _____ and keep the attention of your audience.

Why do you think David is the suitable person for the job?— Because he has higher ambitions _________ others have already been satisfied.

She started studying medicine at college, but ________ to Business Studies in her second year.[ ]