填空题 Early men did not have clocks. They were told time 21
by the sun and shadows of trees. At first time, they used 22
sticks placed in the ground instead trees. They made 23
marks in the ground, and the shadows from the sticks told 24
the time of day. Later, men began to use sundials. Some of 25
sundials were boxes with sticks cast a shadow. Men were 26
able to take the sundial box with them. The mark for noon 27
was very important. The sundials always have to face the same 28
way or the time was wrong. Sundials were good only on sunny 29
days, not on cloud days. They were the first kind of clock. 30