题目

Read the passage and choose the best answer（根据短文内容，选择最恰当的答案）：Dinosaurs were the dominant land animals for 160 million years, making them one of the most successful groups of animals ever. However, all the dinosaurs that were living 65 million years ago went extinct. About 70% of all animal life on the earth died out. Scientists call it a mass extinction（大灭绝）.Having existed for 165 million years, why did dinosaurs die out? There are many different theories about why this happened. We will probably never know exactly what happened, which means that s5．先后掷两次正方体骰子（骰子的六个面分别标有点数1，2，3，4，5，6），骰子朝上的面的点数分别为m，n，则mn是偶数的概率为$\frac{3}{4}$．