In the given question the correct option is missing, which can be described as follows:
"It transforms binary, null variables into the groups."
These variables are real variables, which could also take up a series of variables, that are either constrained or defined. This can be regarded as a listing. It is used to analyze and convert it, into binary in the following ways, and wrong choices can be described as follows:
In option a, It can't combine, it only converts.
Option b and Option c is wrong because, it can't convert numeric, it only convert binary number to dummy variables.
1. Personally, I always use the same search engine, which is Google. I once opened Bing mistakenly, but obviously returned to Google immediately. Google is my preferred choice because I've used it for such a long time that I've gotten so used to it and cannot change it. The other search engines don't look as appealing to me as Google.
2. Some advantages would be definitely the format of the information you get from a search engine as opposed to the metasearch engine - sometimes, the metasearch engine cannot provide you with complete results or even complete sentences, so you may be left with illegible texts. On the other hand, metasearch engines can give you so much more information than regular search engines.
3. If the credentials seem legit, based on particular rules as to how to write sources used (such as Chicago style, APA, etc.), then you can safely assume the source is credible. If the author wrote everything necessary in his text (especially works cited/links available), you can usually trust that source.