Which of the following is an example of source amnesia?

(a) "I forget what is the capital of Poland, but I think it starts with a W."

(b) "I don't remember where I heard this, but I heard that apricot pits can cure cancer."

(c) "For a while this morning I couldn't remember where I was, but then I remembered."

(d) "I studied the periodic table in high school, but now I forget it."