While RNA is often single stranded,transfer RNA (tRNA)is usually found with some double stranded structure.Which of the following explains this?

A)tRNAs contain self-complimentary stem-loop structures
B)after synthesis,tRNA molecules are hydrolyzed in specific places to allow double stranded structures to form
C)regions of tRNAs become supercoiled,thus forcing formation of double stranded regions
D)tRNAs adopt a form much like Z-DNA allowing double stranded regions to form
E)none of the above