TheeconomyofDallas,Texas,isstronganddiversified.

The megaphone(microphone) makes the voice sound louder because it points sound waves in one direction and keeps them from spreading out in all directions.

The wheels of the first road vehicles were fashioned from crude stone disks.

Some sea urchins海胆 have venomous (toxin) spines

Thefearofsmallpox,whichterrorizedtheeighteenthcentury,hasnoanalogy(likeness)today.