Question words

A: [blank_start]Why[blank_end] do you work at weekends? B: Because I can earn more money. A: [blank_start]Whose[blank_end] pen is this? B: I think it's John's pen. A: [blank_start]How[blank_end] did you get here? B: I took a taxi. A: [blank_start]Which[blank_end] of these designs do you prefer? B: I prefer the design on the left. A: [blank_start]What[blank_end] are you writing? B: I'm writing an important email. A: [blank_start]When[blank_end] did you get here? B: I arrived 20 minutes ago.