良好的学习习惯对于提高学习效果是非常重要的。下面的做法你认为科学的有（ 　）
①功课太多，想学哪门就学哪门 ②遇到不会的难题，马上去请教老师或者同学
③珍惜每一点时间全部用来学习　④根据自己特点，合理安排学习时间与计划
⑤劳逸结合，注意休息

    The customs in different countries are rather different. If I have dinner with a Chinese host, he always puts more food onto my plates as soon as I have emptied it. That often discomforts me greatly. I have to eat the food even if I don't want to, because it is considered bad manners in the West to leave one's food on the plate. I have already noticed that when a Chinese sits at an American's dinner party, he often refuses the offer of food or drink though he is in fact still hungry or thirsty. This might be good manners in China, but it is not in the West at all. In the United States, it is impolite to keep asking someone again and again or insist on his accepting something. Americans have a direct way of speaking, if they want something, they will ask for it. If not, they will say, “No, thanks.” When an American is fed with beer by the host, for example, he might say, “No, thanks. I'll take some diet, Pepsy-Cola(百事可乐) if you have it.” That is what an American will do. So when you go to the United States, you had better remember the famous saying: When in Rome（罗马）, do as the Romans do.