Using a minus sign before a keyword search indicates that a. you're adding a "+" and then a "-"to refine the search. b. it's an optional term within your search. c. you're adding a word to your search. d. the word following the "-" is to be excluded from search.

The correct answer is D, The word following the '-' is to be excluded from the search.

When searching something on any search engine, if we use a hyphen before a keyword, that looks like a minus sign, " - ",  it gives results opposite to that keyword. It will exclude all the searches including that keyword. Similarly, if we use a Plus sign, " + ", before a keyword, it will show us the results containing this keyword.

There are many symbols that are used to refine our search. For example, colon, semicolon, quotation marks, two periods, asterisk, etc are used to refine our search.  

answer(b); ; ; the quantitative or qualitative variable for which the experimenter wishes to determine how its value is affected by the explanatory variable;

the answers are

a, b, c, & e.