What is the best evidence for a three-domain system?

The best evidence for the three domain system is

Sensitivity to Antibiotics

Explanation:

The three domains of life includes :

Archaea - oldest known domain, ancient forms of bacteria.

Bacteria - all other bacteria that are not included in the Archaea domain.

Eukarya - all the organisms that are eukaryotic or contain membrane-bound organelles and nuclei.

Types of evidences for the three domain system are:

1) differences in the sequences of nucleotides in the cell's robosomal RNAs (rRNA)

2) the cells's membrane lipid structure.

3) its sensitivity to antibiotics.

as the gila monster consumes the eggs or young of the desert cottontail and gambel's quail, thus its main food supply is only accessible for a restricted time duration every year. however, for this, the gila monsters exhibit three adaptations, which elevate their survival rate in the desert condition.  

first, is that they possess huge bodies, and can consume greater concentrations of food during a small period. secondly, they require to feed infrequently as they can accumulate fat in their tails. ultimately, their rate of metabolism is very low, so that they can burn their reservoirs of fat gradually.