The rhetorician, Hermagoras of Temnos, is attributed as inventing the "elements of circumstance" which is the foundation of the "Five Ws" in basic journalism. Esperanto asks these questions with "K" words and, as an example of correlation which often appears in the language, answers them with "T" words.

Esperanto 	English
Kiu? 		Who?/Which [person]? 
Kio? 		What?
Kiam? 		When?
Kie? 		Where?
Kial? 		Why? 
Kiel? 		How?
Kiom? 		How many?

Esperanto 	English
Tiu 		That/That person
Tio 		That [thing]
Tiam 		Then
Tie 		There
Tial 		That [reason]
Tiel 		Thus
Tiom 		That [many]

To change a standard sentence into a question, simply place the word "cxu" in front of it. So the phrase gxi estas hundo ("it is a dog") can be changed into a question Cxu gxi estas hundo? ("Is it a dog?").