【正确答案】 A

【答案解析】此题旨在检测动词现在完成时的使用方法。现在完成时可以用于把过去的动作和现在的结果联系起来，用于解释原因，如：
He had gone to Shanghai，and is not-at home at the moment．
They came to business with them at once as they have been friends for a long time．(因为是老朋友，他们立即成交了。)