It is spring and a little boy has terrible allergies. His nose is stuffed with mucus and he has a cough. Why are his mucous membranes producing so much mucus? He is allergic to mucus.
It is a sign that he has a head injury.
Mucus traps pollen so it cannot enter the body.
Mucous membranes always make more mucus in spring.

water is a polar molecule. a chemical bond is a force of attraction between atoms or ions. bonds form when atoms share or transfer valence electrons. atoms form chemical bonds to achieve a full outer energy level, which is the most stable arrangement of electrons. so, false

explanation:

in h2o molecule, two water molecules are bonded by a hydrogen bond but the bond between two h - o bonds within a water molecule are covalent. the greater the electronegativity difference, the more ionic the bond is. bonds that are partly ionic are called polar covalent bonds. nonpolar covalent bonds, with equal sharing of the bond electrons, arise when the electronegativities of the two atoms are equal.

the answer is :

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?

answer: dna

because all cells have genes