A. Discussion of greenhouse effect have usually had as a focus the possibility of Earth growing water and to what extent it might,

B. Discussion of greenhouse effects has usually had as its focus whether Earth would get water and what extent wold be,

C. Discussion of greenhouse effects has usually focused on whether Earth would grow warmer and to what extent,

D. The discussion of greenhouse effects have usually focused on the possibility of Earth getting warmer and to what extent it might,

E. The discussion of greenhouse effects has usually focused on whether Earth would grow warmer and extent that is.

27. In the seventh century B.C., the Roman alphabet was adapted from the Etruscan alphabet,which in turn had been adapted in the previous century from western Greek alphabet, which itself had been adapted earlier in the same century from the Phoenician alphabet.

A. which itself had been adapted earlier