题目

如图中的实线是某时刻的波形图像，虚线是经过0.2s时的波形图像。（1）假定波向左传播，求它传播的可能距离。（2）若这列波向右传播，求它的最大周期。   答案：1）向左传播时的距离为，（n=0，1，2…）。可能值有3m、7m、11m…（2）根据得，在所有可能的周期中，当n=0时的最大，故。解析:略 3、We know the mosquito very well. Mosquitoes fly everywhere. They can be found almost all over the world, and there are more than 2, 500 kinds of them. No one likes the mosquito. But the mosquito may decide that she loves you. She? Yes, she it's true that male mosquito doesn't bite （咬）  and only the female mosquito bites because she needs blood to lay eggs. She is always looking for things or people she wants to bite. If she likes what she finds, she bites. But if she doesn't tike your blood, she will turn to someone else for more delicious blood. Next time a mosquito bites you, just remember you are chosen. You're different from the others! If the mosquito likes you, she lands on your body without letting you know. She bites you so quickly and quietly that you may not feel anything different. After she bites, you Will have an itch （痒） on your body because she puts something from her mouth together with your blood. By the time the itching begins, and she has flown away. And then what happens? Well, after her delicious dinner, the mosquito feels tired. She just wants to find a place to have a good rest. There, on a leaf or a wall, she begins to lay eggs, hundreds of eggs. 1．"Mosquito" means ________in Chinese. A．苍蝇                    B．蜻蜓                       C．跳蚤                    D．蚊子 2．We know mosquitoes very well because_______ A．they can be found easily                   B．they fly here and there C．there are many kinds of them       D．they can fly 3．If the mosquit6 doesn't bite you, it will_______ A．get angry with you                  B．be afraid of you C．make a lot of noise                  D．choose another one 4．The mosquito bites you_______ A．when you're asleep                 B．because you have choose it C．too quickly to let you know        D．but doesn't like you