Taking regular exercise and eating a balanced diet are two important keys good health.A.

问题补充：

Taking regular exercise and eating a balanced diet are two important keys good health.

A. in

B. from

C. of

D. to

答案：

A. in

B. from

C. of

(答案→)D. to

解析：D 考察介词。句义：定期做运动和保持均衡的饮食是保持身体健康的两个关键点。Key意为关键，钥匙；后面接介词to，故答案为D。