2015年8月24日，中共中央、国务院印发《关于深化国有企业改革的指导意见》，要求以提高国有资本效率、增强国有企业活力为中心，做强做优做大国有企业，主动适应和引领经济发展新常态。国家深化国有企业改革是（  ）

①发展社会主义市场经济的内在要求

②发挥国有企业作为现代企业组织形式的要求

③更好发挥国有经济主导作用的要求

④市场在资源配置中起决定性作用的表现

    A lot of people like sports. And some love 1 very much. An elephant can also 2basketball. There is an elephant. Its 3is Toktak. He 4 strong and cute. Many people like 5. Do you know 6? Because 7his free time, Toktak often plays basketball with his long trunk（象鼻）. He 8the sport very much. The basketball looks like a toy to Toktak. It is 9to watch Toktak playing basketball. Do you like the elephant? Let's 10him in the zoo. I think you can have fun there.

在平面直角坐标系xOy中，过原点O及点A（0，2）、C（6，0）作矩形OABC，∠AOC的平分线交AB于点D．点P从点O出发，以每秒$\sqrt{2}$个单位长度的速度沿射线OD方向移动；同时点Q从点O出发，以每秒2个单位长度的速度沿x轴正方向移动．设移动时间为t秒，当t为____时，△PQB为直角三角形．