Could we add a rule clarifying the use of 'which' and 'that'. A lot of people get them mixed up.
"That” restricts the reader's thought, directing attention to a specific bit of information to complete a message's meaning.
“Which” is non-restrictive and introduces subsidiary rather than essential information to the meaning of the sentence.
Pikachu likes the DS that is in the kitchen.
(Pikachu has more than one DS, but he likes the one that is in the kitchen.)
Pikachu likes the DS, which is in the kitchen.
(Pikachu only has one DS, it's in the kitchen and he likes it.)