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
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C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。