Nowadays, you can see many people busy on their smartphones(智能手机) if you look a____. Smartphones make our lives easier. But have you ever thought a____ what they mean to your eyes? Staring(盯) at smartphones for long time gives you dry eyes and even causes a disease ____ (叫做) glaucoma(青光眼).   

    While you're probably not going to stop using your smartphone, there are a few things you can do to protect your eyes. Hold your phone at least 30 cm away from your eyes when using it. Take a break every ____ (小时) and try the following: look at something at least five meters away from you and then focus on the tip of your nose. Repeat this s____ times. It should reduce(减少) the discomfort in your eyes.

明代中后期，江南地区出现了“机户出资，机工出力”的现象。这里的“机户”和“机工”是

关于气体的性质，下列说法正确的是（）

下列属于珠江三角洲生产的产品的是（　　）

①电子电器    ②机械    ③日用消费品    ④造船