You Want to Design a Set of PCR Primers to Amplify

You want to design a set of PCR primers to amplify a portion of a gene from a cDNA library.Which of the following concerns about PCR primer design is the most legitimate?

A) You must be careful when designing your primers to take into account which DNA strand was transcribed in mRNA and make sure both primers are complementary to the mRNA.
B) You must be certain not to include any DNA sequences in your primer that are upstream (5′) of the AUG start codon.
C) You must make sure that all the DNA sequences in your primer lie within an exon, and do not span two exons.
D) You must be certain that all the DNA sequences in your primer are not located downstream (3′) of the polyadenylation signal.