According to the passage, the more protein a rat consumes, the lower will be the
A.
ratio of the rat' s blood-tryptophan concentration to the amount of serotonin produced and released in the rat's brain.
B.
ratio of the rat's blood-tryptophan concentration to the concentration in its blood of the other amino acids contained in the protein.
C.
ratio of the rat's blood-tyrosine concentration to its blood-leucine concentration.
D.
number of neurotransmitters of any kind that the rat will produce and release.
E.
number of amino acids the rat' s blood will contain.