Receptors detect presence of acids in substances, whereas receptors detect sodium in substances.
a.
sour . . salt
b.
sweet . . bitter
c.
bitter . . salt
d.
sweet . . sour

Answer) The answer for the fill in the blanks is A) Sour. .salt

Any eatable substance possesses variety of taste like bitter, sweet, salty, salt etc. Almost all animals can easily sense this.

Taste receptors are responsible for sensing taste. They are present on the tongue in the form of clusters called as taste buds. These receptors get activated once the food with specific taste is ingested by the organism. Sour receptors detect the presence of acids in substances, whereas salt receptors detect sodium in substances.

the fossil record provides evidence of a common ancestor to many species.