题目

Tayka Hotel de Sal Where: Tahua, Bolivia How much: About $ 95 a night Why it’s cool: You’ve stayed at hotels made of brick or wood, but salt? That’s something few can claim. Tayka Hotel de Sal is made totally of salt---including the beds (though you’ll sleep on regular mattresses and blankets). The hotel sits on the Salar de Uyuni, a prehistoric dried-up lake which is the world’s biggest salt flat. Builders use the salt from the 4,633-square-mile flat to make the bricks, and glue them together with a paste (糊) of wet salt that hardens when it dries. When rain starts to dis已知a=（-3，4），b=（5，2），则a·b等于（    ）A.23          B.7           C.-23         D.-7