完形填空。阅读下面短文，掌握其大意，从每题所给的A、B、C、D四个选项中，选出最佳选项。
Behind our house is the start of a fascinating trail (小径). This trail is one of the old roads that wind through untold miles of forest. My 1 , Beans, and I walk the trail frequently. Normally, Beans sniffs alongside the 2 to follow the smell of a deer track or 3 some cause known only to him.
