已知,$\overrightarrow{a}$·$\overrightarrow{b}$=-3，则$\overrightarrow{a}$与$\overrightarrow{b}$的夹角是(    )

动物界中最高等的动物类群是（    ）

根据短文内容完成下列任务。

Cindy is my friend. She likes sports very much. She runs (跑步) every morning. Cindy is healthy and she eats well.

For breakfast, she likes eggs, bananas and milk. For lunch, she has chicken, tomatoes and vegetables. She likes fish, salad and carrots for dinner. She eats oranges, pears and apples, too. 水果和蔬菜是健康食品。She doesn't like ice-cream. And she doesn't eat hamburgers or French fries (薯条). They are not healthy food.

求证：a²＋b²≠c²

1914 年 6 月 28 日，德皇威廉二世的朋友奥地利皇储弗朗茨•斐迪南大公在萨拉热窝被 刺身亡。得知还有的死讯后，威廉大为震惊。于是，他向奥匈帝国提供协助，支持其镇压策划刺杀行动的秘密组织，甚至容许奥国以武力对付怀疑是该组织的幕后黑手──塞尔维亚。 对此材料的深层含义解读最为恰当的是（    ）