17 The indicator cresol red changes from red to yellow when put into an acid.

Some blocks of agar containing cresol red were cut to different sizes and put in an acid. All other

variables were kept constant. The blocks were measured in mm.

Which block became completely yellow most quickly?

A 3 × 30 × 30

B 6x6x6

C 6 x 12 x 12

D 12 x 12 x 12