The host prepare usucha when he prepares the charcoal for the second time.
Answer: Option B
Step-by-step explanation:
The first time the host prepares the charcoal to make something to serve and take for the guests, he makes koicha. Koicha is a form of tea but this form of tea is thick.
Then after making koicha, he again prepares the charcoal to make something. Second time also he makes a kind of tea but that is not thick tea, it is thin tea. This is known as the usucha. Usucha is not the same as koicha even though they are both types of tea only.