Fill in all the gaps, then press "Check" to check your answers.

taxi / Whose / this/ is / ?
?	It's Professor Smart's taxi.
mouse / is / this / Whose / ?
?	It's mouse.
cat / Whose / this / is / ?
?	It's .
Whose / is / that / pen / ?
?	It's .
that / is / book / Whose / ?
?	.