Investigation is one of the common methods of scientific inquiry. First of all, it is necessary to clarify the purpose and object of the investigation and formulate a reasonable investigation plan. Sometimes, because of the large scope of investigation, some respondents should be selected as samples. When investigating, it shall be recorded truthfully. The survey results should be sorted out and analyzed, and sometimes they should be counted by mathematical methods. There are two kinds of surveys: general survey and sampling survey. In order to understand the problems of bean sprouts, the Ministry of Agriculture selected samples of bean sprouts sold in some provinces and cities in April.

So choose: a