摘要： how long/how often how long意为“多久 .“多长 .用于提问时间或距离的长短.如: How long were you away last year? 去年你缺席多长时间? How long is the Great Wall? 长城有多长? how often意为“每隔多久.每隔多长时间 .回答表示程度的频度副词有sometimes, always, usually, never等或once a week, three times a month等.如: How often do you go to see your mother? 你每隔多长时间去看你的母亲? 此外.how far意为“多远 , how old“多大 , how many“多少 .
Colour helps you see things．But man and some monkeys and apes(猿) are the only mammals(哺乳动物) that can see colour．1 any other mammals，such as the dog，the world 2 a black-white photo．Dogs hunt mainly by listening and smelling．
Like 3 animals，dogs see best when things move．The animals they hunt seem to know this．A rabbit or deer will freeze when they find that they are being hunted．Then the dog 4 see it at all
Birds can see colour．They need to，because when they fly，they need to find places to land．Colour helps them know 5 the place is and what it is like so that they are able to catch flying things in the air or to 6 something they think safe．
Some birds see things even 7 than man．The birds that eat bugs(虫子) can see them from far away．And even a very young bird can see a house 8 the sky．So good eyes and being able to see colours help birds 9 food and also help them find out 10 there are other animals that are dangerous to them．