What is the dna backbone made of?
- a nitrogenous base and a sugar molecule
- nitrogenous bases, sugar, and phosphates
- sugar and phosphates
- a polymer of nitrogenous bases

What is a coast of using technology to transport water? a. cities can be built in otherwise uninhabitable areas. b. crops can be irrigated and grown in new areas. c. floods can be averted in flood-prone areas. d. freshwater supplies can be depleted in an area.

Which best explains how a heat pump can heat a room? cold air from the house is moved through pipes, where it absorbs thermal energy. warm air from outside is pushed into the house to replace the cold air. combustion warms the air when chemical energy is transferred to thermal energy. fuel is used to move a piston, which pushes warm air into the house.

Which of the following describes a negative feedback loop? when the heart rate is too high, the body sends hormones that continually increase the heart rate higher. when a pregnant woman is in labor, the body sends hormones that increase the intensity of contractions, which then increases the secretion of the same hormones. when blood sugar is too low, the body sends hormones that raise blood sugar until it reaches a typical level and hormone secretion slows. when a person is jogging, the body sends hormones that continually decrease the rate of oxygen supply to the legs.