Explain briefly why a sample survey is usually preferred over census survey? ?

it's because a sample survery is like a rough draft, that people can use and turn it in to get an easy 100 grade also... A survey based on a portion of the population is called a sample survey. A sample survey is preferred over a census for the following reasons: Conducting a census is very expensive because the size of the population is usually very large.

probably 3 since archeologists and historians don’t understand there writing.

well this isn't a question but if you are asking if it is true or false it is, true.