某同学在没有电流表的情况下，利用电压表和已知阻值的定值电阻R₀，测量未知电阻R_x阻值，图中可实现测量R_x阻值的正确电路图是（  ）

关于四种光学仪器的成像情况，下列说法中正确的是（   ）

    Hello, everyone! Tomorrow we'll go for a trip in the mountains. Before we start, there are some ____ and suggestions for you. First, everyone should ____ sports shoes. Second, when you walk in the mountains, you mustn't walk too ____ "to the edge of the path. Third, you must keep ____ or you'll get lost. Fourth, bring some water with you, or you'll be ____.

    We need to put up a tent to stay at night in the mountains. Be careful of the ____ when you are in the forest. Although some animals look ____ they are really dangerous. If you meet animals, don't move suddenly. Just keep still until they ____. Remember to hang your food in the tree before you go to sleep Hope everyone can have a good trip.