S7. When you are breathing hard and unable to engage in conversation, that means you are ______.

A．It is very simple to operate.
B．It does not produce pollution.
C．It costs quite a bit of money to use.
D．It can replace cars in crowded city centers.

A．To have them replanted in fields.
B．To control how fast the trees grow.
C．To give the trees the traditional shape.
D．To remove the unwanted from the trees