John is such a(n) ________ boy that he doesn't want to do any work.

京张铁路为中国铁路事业开创了新的方向。“新方向”是指      (　　)。

下列代数式中，符合代数式书写要求的有____ 

（1）ab÷c²；（2）$\frac{3m}{n}$；（3）3$\frac{1}{5}{x}^{2}y$；（4）3×（m+n）；（5）$\frac{a^2-b^2}{5}$；（6）ab•3

Shelly had prepared carefully for her biology examination so that she could be sure of passing it at her first ________．（   ）