(a) Nitrogen
(b) Carbon dioxide
(c) Oxygen
(d) Water vapor

(a) All materials are attracted to magnets.
(b) Magnets only attract metals.
(c) Magnets attract materials with similar poles and repel those with opposite poles.
(d) The reason is still unknown.

(a) They kill existing pathogens.
(b) They train the immune system to recognize pathogens.
(c) They directly destroy infected cells.
(d) They provide immediate relief from symptoms.

(a) Increases
(b) Decreases
(c) Stays the same
(d) Depends on the type of gas

(a) Changes in the moon’s phases
(b) Earth’s rotation on its axis
(c) Earth’s revolution around the sun
(d) The tilt of Earth’s axis

(a) Burning of oxygen

(b) Rapid movement of charged particles

(c) Reflection of sunlight

(d) Chemical reaction between air and water

(a) Breaks down carbohydrates

(b) Breaks down proteins

(c) Neutralizes stomach acid

(d) Absorbs nutrients

(a) Stays the same

(b) Changes from solid to liquid

(c) Changes from liquid to gas

(d) Particles generally slow down and move closer together

(a) Exposure to sunlight

(b) Growth of mold spores

(c) Change in temperature

(d) Lack of water