Multi-choice problem: Continue writing the next sentence in this paragraph:

First someone says something and then he starts twisting sides of the cube to match the colors together. when he

Available choices:
[a]. is finished he has a green square in front of the cube and he starts to measure it and then place it in the open square to the side with his fingers.
[b]. 's done, he turns the cube in different ways to show viewers how all of the colors are grouped together.
[c]. finally squares it in, he shows the cube and puts it in the middle.
[d]. is done, he has the blue cube inside his shirt and he is pleased with his work.
[b].