Final answer:
The type of pasta similar to vermicelli with a smaller diameter is Angel hair. Among the options provided, it is the thinnest pasta and is used in delicate dishes, whereas the other types have distinct shapes and culinary uses.
Step-by-step explanation:
The type of pasta that is similar to vermicelli but has a smaller diameter is a) Angel hair. Angel hair pasta is very fine, long strands of pasta that cook quickly and are often used in light sauces, like a simple tomato sauce or broth. Compared to vermicelli, angel hair is thinner and lends itself to more delicate dishes. Other pasta types like fideo, campanelle, and rotini have different shapes and uses. Fideo is typically used in soups or as a noodle-like component in certain dishes, campanelle has a bell-like shape and is great for holding onto sauces, and rotini is a corkscrew-shaped pasta that's excellent for pasta salads and hearty sauces.