a) How do they determine the load limit for bridges?
They drive progressively heavier and heavier trucks over the bridge until it breaks. Then they weigh the last truck and rebuild the bridge.
b) How do people make babies?
Most people just go to Sears, buy the kit, and follow the assembly instructions. However, Calvin was a K-Mart blue light special-- almost as good and a lot cheaper.
c) Why does the sun go east to west?
Solar wind.
d) Why does the sun turn red at sunset?
When the sun comes down to Earth's atmosphere, all the oxygen catches fire.
e) How do lightbulbs and vacuum cleaners work?
Magic.