【正确答案】 B

【答案解析】[理由] 本句测试与过去事实相反的虚拟语气，结构如下：
If+主语+had+过去分词，
[*]
如果当时……的话，就会/应该/可以/可能会……了
[例] If you had met him yesterday, he would have told you the truth.
(如果你昨天遇到他的话，他就会跟你说实话了。)
If I had had time yesterday，I would have gone to the beach with you.
(如果我昨天有空的话，就会和你去海边了。)
此时的If从句也可将had置于句首，故上列两个例句皆可改写如下：
Had you met him yesterday, he would have told you the truth.
Had I had time yesterday, I would have gone to the beach with you.
根据上述，原句句首“Had he set out...”等于“If he had set out...”，故知此为与过去事实相反的假设语气，因此(B)应为正选。