Is a specific system for gathering information from a single group of respondents by continuously monitoring the advertising, promotion, and pricing they are exposed to and the things they buy.

The answer is "Scanner based research".

Explanation:

A scanner focused testing method allows advertisers to track the exposure and response of a consumer panel to variables like ads, promotions, store displays, packaging, and quality.  

which functions return a valid value without any arguments?

(-blank- and -blank- return a valid value without any arguments.)

1st -blank-

today

sqrt

count

2nd -blank-

round

now

sqrt