17. what's mass?
a. a measure of an element's attraction for electrons
b. the force that gravity exerts upon an object
c. the sum of the number of protons and neutrons in an atom
d. a measure of the amount of matter an object contains

Which of the following are causes of coastal erosion? check all that apply. beach grasses and other plants trap windblown sand. wave action carves away the coastline. groundwater under pressure is forced to earth’s surface. artificial structures stop the natural flow of sand along the coast. underground caves collapse as bedrock is dissolved.

Epinephrine is a hormone released from the adrenal gland of the body, most often in a stressful situation. it is known as the "fight-or-flight" hormone. one way that it causes a response in the body is to activate receptors on muscle cells. where are these cellular receptors located? a. on the cell membrane b. in the nucleus c. on the cell wall d. around the mitochondria

Identify the various levels of atmosphere. troposphere mesosphere exosphere stratosphere thermosphere