比尔·盖茨曾经说过这样一句话：你甚至不知道和你交流的对方是人还是一条坐在电脑前会敲击键盘的狗。这告诉我们（  ）

①网络交往中可以畅所欲言，无拘无束    ②网络交往对象具有虚拟性、间接性和隐蔽性

③青少年上网有利无弊                           ④网络是把双刃剑，我们要学会抵制不良诱惑

    I like school days. I can learn many things from school. We have four classes in the morning and two in the afternoon. I like weekends, too. We don't go to school on Saturdays and Sundays. I often play ping-pong and play basketball on Saturday morning. I often play the violin (小提琴) on Saturday afternoon. I often do homework and play football on Sunday morning. I often go to the park on Sunday afternoon.

某地大量捕杀青蛙，结果虫灾暴发，粮食减产，造成这种现象的直接原因是：

珠江三角洲地区经济发展的特点是（　　）