William Henry Harrison, the ninth President of the USA, was born in a small town. When he was a boy, he was very quiet and shy. Because he was so quiet, everyone thought that he wasn't bright. People in the town often put a nickel(五分镍币)and a dime(十分硬币)before him and asked him which to choose. He always chose the nickel and they laughed.

    One day a woman felt sorry for him. She asked, "Why do you never take a dime and always choose a nickel? Do you know a nickel is worth(值……钱) much less than a dime?"

    "Certainly I know it.” William answered slowly. "But if I choose the dime, they will not ask me to choose them any more.”

计算：

（1）$\frac{1}{5}$$\sqrt{30}$×$\sqrt{\frac{1}{5}}$×（﹣$\sqrt{3}$）                     

（2）$\sqrt{12}$+3$\sqrt{\frac{4}{3}}$﹣$\sqrt{5\frac{1}{3}}$﹣$\frac{2}{3}$$\sqrt{48}$．

如图，空间四边形ABCD的对角线AC，BD相等，顺次连接各边中点E，F，G，H，则四边形EFGH一定是（　　）