Пищевая цепочка, в которой участвует колибри.

помогите

В равносторонний треугольник, сторона которого равна 16 см, вписан другой треугольник, вершинами которого являются середины сторон первого. Во второй треугольник таким же способом вписан третий и т. д. Докажите, что периметры треугольников образуют геометрическую прогрессию, и найдите периметр шестого треугольника

рассчитайте массы гидроксида натрия и воды, которые необходимо взять для приготовления 50г раствора щелочи с массовой долей гидроксида натрия 20%.

особливість будови пінгвінів,яка відрізняє їх від інших видів птахів

I. Use the correct tense-forms of the verbs in brackets. 
1. If the weather (keep) fine we (stay) here until the end of the month. 
2. She said she already (buy) all the Christmas presents. 
3. I (know) him for seven years. We (study) at school to¬gether. 
4. I (turn) round and (see) a girl at the far end of the street. She (call) for help. 
5. What you (think) of the chairman's report?-The facts (sound) very convincing 
6. I don't think the weather (change) for the better. But if it (do) we (go) on an outing. 
7. No one knew that David (do) research on this problem for nearly two years. 
II. Choose the right article. 
1. ..robbers had left by ...time the police arrived. 
2. What were you doing when you heard ...news? 
3. When you are typing ...letter remember to type ...date at... top and to sign your name at... bottom. 
4. It's ...best salad I've ever eaten. Can you give me ...recipe? 
5. When ...door-bell rang, he just stood near for... moment before opening it. 
6. Anyone can make ...mistake. 
III. Choose the suitable preposition. 
1. Why are you (in, on, by) such a hurry? 
2. It hurt the eyes to look (on, at, in) the sun. 
3. I've bought this cake (on, to, for) your birthday. 
4. I always finish work early (in, on, at) Fridays. 
5. How many cinemas are there (in, on, at) this town? 
IV. Choose the suitable pronoun. 
1. We study almost (every, some, no) day. 
2. I have two packs of cards. One is on the table, (another, other, the other) is in the drawer. 
3. (Nobody, Any, Someone) can do it but you. 
4. I think rock music is just (a lot, many, much) of noise. 
5. There's hardly (some, any, no) tea left. 
V. Put the words in the right order to make up a sentence. 
1. broken/window/when/the/was? 
2. when/bus/ waiting/the/we/accident/an/were/for/we/saw. 
3. want/a/be/he/still/does/to/policeman? 
4. to/a/quite/had/we/go/way/long. 
VI. Choose the right variant. 
1. I'm awfully sorry. 
a) Don't mention it. 
b) That's O.K. 
c) It serves you right. 
3. Could you pass me the paper? 
a) Yes, I could. 
b) Yes, I will. 
c) Here you are. 
2. How are you? 
a) Don't worry. 
b) And how are you? 
c) I'm fine, thank you. 
4. Will you open the drawer for me? 
a) What do you want? 
b) Do it yourself. 
c) Sure, no problem. 
VII. Choose the appropriate word. 
This summer is (so, such) hot. London is already (full, filled) of tourists and (there, it) is (heavy, hard) to find room to walk (along, across) the pavement in some areas, (especialy) specially) in Piccadilly. It's (almost, rather) impossible to work in this (hot, heat). Most of the time we (drink, eat) iced cokes in the office and (fun, fan) ourselves with pieces of (typed, typing) paper.