Because of the High Temperature _____ Step During a PCR $\lambda$

Because of the high temperature _____ step during a PCR reaction, the DNA polymerase from _____ is used.

A) primer extension; E. coli
B) strand separation; Thermus aquaticus
C) primer annealing; Thermus aquaticus
D) primer extension; bacteriophage $\lambda$
E) strand separation; E. coli