Since the 1990s, HIV transmission rates among intravenous drug users have been reduced from about 50% to about 10%. According to the text, which of these factors led to this decrease?

The term that refers to an individual's genetic make-up is __________; the term that refers to the physical characteristics that result from that genetic make-up is __________:

a. autosomes; gametes b. gametes; autosomes c. phenotype; genotype d. genotype; phenotype

The cerebral cortex in humans accounts for what percent of all the neurons in the central nervous system?

a. 10 percent b. 40 percent c. 70 percent d. 99 percent