Many anti-cancer drugs are often first tested on cells cultured in vitro.Which of the following statements may BEST explain why these in vitro tests do not always predict clinical response to these drugs?

A)Cancer cells grown in vitro do not proliferate as readily as they do in vivo.
B)Cancer cells grown in vitro are always anchorage-independent.
C)The conditions of in vitro culture do not recapitulate the effects of the stromal compartment of tumors operating in vivo.
D)A and B.
E)A and C.