Thallium has two isotopes: thallium-203 and thallium 205. Thallium's atomic number is 81 and its atomic mass is 204.38 amu. Which statement about the thallium isotopes is true?

A.There is more thallium-203 in nature.

B.Atoms of both isotopes have 81 neutrons.

C.Thallium-205 isotopes have fewer neutrons than thallium-203 isotopes.

D.All atoms of thallium have 81 protons.