Which greenhouse gas released by refrigerators and air cooling systems causes global warming?

a. nitrogen oxide
b. carbon dioxide
c. chlorofluorocarbons

If the singular term ends in -us, the plural is usually formed by changing the ending to

Which behavior of an expectant mother is unhealthy

Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell? a) herpesb) aidsc) smallpoxd) influenza