下列各句中，没有语病的一句是(　　)

It is generally believed that teaching is _____ it is a science.

It’s more than half a century _________ my grandfather joined the Party and became a servant to the people.

Jack is the ______- child in the family;he wants to have a brother

I don’t understand why the boss should __________ thegirl, because in my opinion, it was her fault that caused the loss.