Which characteristics do all terrestrial planets have? select all that apply.

a. water
b. iron core
c. rocky crust
d. thin atmosphere
e. dense atmosphere
f. relatively high density

"Terrestrial" means 'on Earth' or 'like Earth'.

The so-called 'terrestrial planets' are Mercury, Venus, Earth, and Mars.
The asteroid belt separates them from the 4 gas-giant planets, in a wide
gap where there should be another planet but there isn't.

Among the terrestrial planets as a group:

A).  Water
       No.  Only earth has water (now).

B).  Iron core
       Yes.  Most probably all.

C).  Rocky crust
       Yes.  All.

D).  Thin atmosphere.
E).  Dense Atmosphere.
       No. 
       Only Venus has a dense one.
       Mercury probably has none.
       Earth has the Goldilocks atmosphere.

F).  Relatively high density.
       Yes. 
       True of all the terrestrial planets.
       Earth is the most dense of all the planets.      

B. a circuit. i think