【单选题】Today, bicycles are elegantly simple machines that are common around the world. Many people ride bicycles for recreation, whereas others use them as a means of transportation. The first bicycle, calle...
A.
The safety bicycle would look familiar to today’s cyclists.
B.
Two hundred years ago, bicycles didn’t even exist.
C.
The Michaux brothers called their bicycle a vélocipède.
【简答题】It is interesting to see that the force of only 6 or 7 people pushing in the same direction can cause up to 1,000 pounds of force—enough to break brick walls.During a deadly stampede( 奔逃 ) , people ca...