17. Read the statements and ask what is not clear to you.

17. Read the statements and ask what is not clear to you.

1) Concrete was made of clay and later of gypsum and lime. (Why?
When? )

2) The first reinforced concrete skyscraper was built. (When? Where?
How many? )

3) It is difficult to imagine modern structure without concrete. (Why?
What? )

4) Many types of concrete are used in construction. (What? )

5) The use of concrete and reinforced concrete is almost universal.
(Where? What? )

6) There are two kinds of reinforced concrete. (What? Where? )

7) Prestressed concrete is not subject to cracking. (Why? What? Where? )

8) There is a broad division of concrete types into dense and light-weight
concretes. (What? )

9) Some concretes are made by using materials which foam. (What? ) ^:

10) Cellular concretes have very light weight (Why? What? )