问题补充：
The experiment shows that proper amounts of exercise, if regularly, can improve our health.
A. being carried out
B. carrying out
C. carried out
D. to carry out
答案：
A. being carried out
B. carrying out
(答案→)C. carried out
D. to carry out
解析：：本题考查if条件句中的省略情况。本句的句子的主语是the experiment；谓语动词是shows；that引导宾语从句，宾语从句的主干事：proper amounts of exercise can improve our health，if regularly是插入的条件从句，从句的主语是proper amounts of exercise，此时应用it代替前面提到的主语，条件句的主语与主句的主语一致，并且含有is，故省略了it is，完整形式是：if it is carried out。句意为：这项实验表明，适当的运动，如果有规律的进行，能够有助于我们的身体健康。
