Melanie has become increasingly preoccupied with worry about all kinds of things, ranging from whether she left her oven on to terrorism to how it might look if she trips in the grocery store, the last of which eventually causes her to avoid all stores in general. she tends to engage in a variety of behaviors that she describes as “superstitious,” including making sure she always locks her door exactly five times when she leaves her house. she also has trouble sleeping and concentrating and is very irritable. what type of disorder best identifies melanie's symptoms?