Хочу спросить что означает это слово? какой вариант правильный и почему: what this words means? what does this words mean? и еще когда нельсон мандела стал президентом юар? when nelson mandela became a president of south africa? или when did nelson mandela become a president of south africa? что сказал учитель? what did the teacher say?

What does this word mean?
when did Nelson Mandela become?
what did the teacher say?

1. I prefer to travel by horse and by train
2. I'm very scared to use cars and aeroplanes
3. In my country average lifespan is about 70 years
4. I can't do a lot to help smb
5. I'd love to live in the countryside
6. to be full of huge blocks of flats. 
7. I want to be far apart from each other. 
8. It's take a long span of time to communicate by writing to each other.
9. I don't like to communicate by telephone.
10. I don't want it to be a very major change in my life. 
11. this invention will take place one hundred years in the future

1. The book is..on/in the table. 2. The lamp is..on.. the table. 
3. The girl is...at the table. 4. The man is...on the chair. 
5. The book is...in  the bag. 6. The pencil is...under/on the desk. 
7. My house is ...in the street. 8. The blackboard is ...in the 
classroom. 9. The chair is ...by/at the table. 10. We sit ...at the 
table. 11. There is a lamp ...near/on the desk. 12. Please, sit 
down ...at the table. 13. A sport ground is ...behind our school. 
14. Pushkin street is ...between Lenin street and Sadovaya street. 
15. We have lunch ...between 11 o'clock and 12 o'clock. 16. The 
bridge is ...over/across the Don River.