Which of the following best describes the climates of Europe and North America during the 1.8 million years of the Quaternary period?

hot and dry
cool and rainy periods followed by droughts
warm and mild
a series of ice ages followed by periods when the glaciers melted

Which of the following statements about extinction is true?

Extinction can only be caused by human-induced activities.
Extinction can only be caused by natural activities.
Extinction can be caused by human-induced activities or natural activities.
Scientists do not know what causes extinction.

During radioactive decay, atoms of a radioactive element break down and change into other atoms of another element—all at once.
true
false

My answers:
1. D
2.C
3.True