The answer is D: I looked under the bed -- can you believe it? -- and there it was!
A dash is used in English both in formal and informal writing. They should not be overused. The usual recommendation is, in informal writing, to use not more than two in a sentence, and in formal writing, not more than two per paragraph. Dashes are most commonly used to change the topic within a sentence or to add surprising or unexpected information to complement the sentence, like in this example. When using dashes one should abide by common grammatical rules in order to express sense in a meaningful manner.