It's a fine day. The Black（布莱克一家）are busy today. Tony and Gogo are going to the beach. Jenny is going to the park with her friends. Mrs. Black is going to the shopping mall. She is going to buy some milk and vegetables. Is Mr. Black going to the shopping mall, too? No, he isn't. He's going to stay at home. Look! He is reading the newspapers（报纸）.

若方程组$\left\{\begin{array}{c}3x+5y=m+2\\ 2x+3y=m\end{array}\right.$的解x与y的和为0，则m的值为（　　）

我们处在一个有声世界里，不同场合，人们对声音的音量会有不同要求．音量大小的单位是分贝（dB），对于一个强度为I的声波，其音量的大小η可由如下公式计算：η=10lg$\frac{I}{I_0}$（其中I₀是人耳能听到的声音的最低声波强度），则70dB的声音强度I₁是60dB的声音强度I₂的（　　）