对
4) A frame of reference is necessary to describe motion accurately because it provides a fixed point against which motion can be measured.
选择一项：
对
错
1) The background is called the frame of reference when discussing motion.
选择一项：
对
错
2) Change in position is referred to as _________.
a.
motion
b.
frame of reference
c.
reference point
d.
turning
3) It is possible for a person to movie in more than one direction at a time.
选择一项：
对
错
1 answer
1 answer