单选题 Our research has focused on a drug which is so ______ as to be able to change brain chemistry.
A. powerful B. influential C. monstrous D. vigorous

【正确答案】 A
【答案解析】[解析] A．powerful强大的；B．influential有影响的；C．monstrous畸形的；D．vigorous精力旺盛的。