Work Step by Step
An ORF must have a place where cellular machinery can start to read and transcribe DNA (B.), which, in turn, requires a start codon. This disagrees with the answer in the book, which, in turn, disagrees with the text on p. 362, upper left hand column--books sometimes contain errors. A stop codon (A.) is not necessarily required since the machinery will read DNA without it, and the sequence need not be a given length (C.). Since A. and C. are wrong, so it D. If you do accept that the stop codon and a certain length (A. and C.) are required, then D. is the correct answer, as the book says.