is one of the four great inventions of ancient China.
There isn't ______ in the classroom. Let’s turn off the lights.
Something was wrong with my bike, ______ I was late for school.
—Where is your Chinese teacher? —He’s ______the meeting room.
—Who is that lovely girl? —______ is my sister.
—Excuse me, can you tell me ________? —Sorry, I’m a stranger here.