GRE Questions

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A Telephone or an Alarm...

Economic resources include land, labour, capital and entrepreneurship. 

Entrepreneurship is also considered an economic resource because individuals are responsible for creating businesses and moving economic resources in the business environment.

These economic resources are also called as Factors of production.

For the given problem there are three possiblities.
Father's age can be = 36, 31, 29
Mother's age = 32, 27, 25
Son's age = 8, 3, 1.

By using only B it can be calculated.

Maps.

Therefore the answer for What travels around the world but stays in one spot is STAMP or any other thing that acts as a stamp does.

Ex. the letter in the envelope etc...

Since, Several things have the possibility, but the word travel evokes that it would move. 

The second would employ a comma, or semi-colon, and not a colon so it is not properly punctuated.

The third sentence would not be correct because it uses 'like', usually used for comparison. Since you are not comparing two questions, it would not be appropriate.

The fourth sentence has 'is' before the colon, which is a implies declaration and not listing. So, again, it would not be appropriate.

Hence, the first sentence, however, is punctuated correctly.