Which statement best describes the human respiratory system? A) It is composed of a network of moist passageways that permit air to flow from the external environment to the lungs. B) Each cell of the human body is in direct contact with the external environment, and gas exchange occurs by diffusion. C) The external body surface is kept moist to allow for gas exchange. D) Gases diffuse across membranes on both the external and internal surfaces of the body.

Which of the following sex and generation combinations directly produces the pollen tube of angiosperms? a) male gametophyteb) female gametophytec) male sporophyted) female sporophyte

How many major plates cover the earth

Two students are working together on an experiment that measures the effect of different liquid fertilizers on the thickness of plants’ stems. which is most likely to result in the greatest amount of error in their scientific experiment? a.one student measures the plant stem widths by using calipers. the other student measures the widths of the same plant stems again by using a different pair of calipers. b.one student measures the plant stem widths by using calipers. the other student types the measurements as they are taken into a computer spreadsheet. c.one student weighs liquids for the experiment by using a calibrated scale. the other student weighs liquids for the experiment by using a different calibrated scale.