Two types of countries have low rates of teenage pregnancy: those that are very restrictive in sexual behavior and those that are ____

Repeated use of drugs over a period of time can result in a need for a higher dose to get the intended effect. This condition is known as:

a. addiction. b. dependence. c. withdrawal. d. tolerance.

One parent can produce about ___ different combinations of chromosomes, and the two together can produce about ___

a. 8 million, 60 to 70 trillion b. 100 million, 250 trillion c. 2 billion, 750 trillion d. 1 million, 6 trillion