单选题 Surgeons are using robotic systems to perform an ever-growing list of operations, not because the machines save money ______, thanks to the greater precision of robots, the patients recover in less time and have fewer complications.

A. not because
B. but
C. but because
D. but for

【正确答案】 C

【答案解析】[解析] 根据句意以及提示词“not because”可知，该空表达转折，故选择but because。此处使用了“not...but”结构。