Answer:
The detail that does not support of fit into this paragraph's main idea is:
B) Dogs are delightful pets indeed, but they also require a lot of responsibility.
Step-by-step explanation:
The instructions in "How To Set Up a Fish Aquarium" are clear: they concern fish and aquariums. They do not, at any point, concern dogs. All of the other options mention something that does have a connection with the paragraph: the amount of water to put into the aquarium, how thick the pebble layer at the bottom should be, the right type of decorations to be used. However, the second option says that having a dog requires a lot of responsibility. It doesn't say anything about the dog that could be connected to having an aquarium, such as making sure that your aquarium can't be knocked off the table by a big dog of something of the kind. Thus, letter B is the one that does not fit into the paragraph's main idea.