Which of the following describes a response to external stimuli ?
a. a boy sneezes when exposed to a cat dander.
b. a girl eats food when she is hungry.
c. a child becomes hyperactive do to a chemical imbalance.
d. a person yawns when oxygen levels in the blood are low.

Saliva, sweat, pee, and dander (dead skin cells) can all trigger allergies. Pet fur also traps mold, pollen, and other outdoor allergens that make you sneeze and your eyes water.

Explanation:

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

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