Today we are sure that the mail will be sent every day to
our door. But in the early days, no one could be sure about where—or when—the
mail would arrive. There is a stump (树桩) of a big tree in the
state of Washington. It was once a "post office". Because people needed a place
for the mail carder (信使) to leave their letters, they found a tree at the cross
of roads and cut it down ten feet from the ground. Then they hollowed it
out and covered it with something. Inside, they put many boxes. Each box had
a family’s name on it. The mail carder could leave letters there for
everyone. Even earlier, when there was no post services, people
gave their letters to any traveler going in the right direction. Often they gave
them to a traveling shoe maker. The traveler might stop in a small hotel and he
would leave the letters there. But the letters stayed there until the person to
receive them happened to come by and stop at the hotel. Today
an airmail letter can travel across the world in much less time than that. And
you know that your letter will go where you want it to go, and when. What does "hollowed it out" mean in "Then they hollowed it out..."
A.Made its inside empty.
B.Covered its stump up.
C.Cut it short.