参考答案：B

解析：[听力原文]Since the wedding march for gays and lesbians began in San Francisco three weeks ago, officials in California, New Mexico and Oregon have allowed same-sex marriages, Massachusetts has signaled its approval. President Bush has called for a constitutional amendment to ban gay marriage. Lawmakers conservative, and gay-rights groups have all joined a debate that has roiled the nation.

[分析]： 对信息的推断。 原文中提到California, New Mexico和Oregon允许同性婚姻，而“Massachusetts has signaled its approval”，即“Massachusetts发出同意的信号”，由此可推测，虽然Massachusetts不反对同性婚姻，但还没在法律上正式承认。因此，选项b的说法是正确的。[解题关键] 掌握主要短语的深层含义，如signaled its approval表示对某事并不反对，但尚未公开承认的状况。