Indicate whether each of the following mobile elements in Drosophila is a DNA-only transposon (D), a retroviral-like retrotransposon (R), or a nonretroviral retrotransposon (N). Your answer would be a four-letter string composed of letters D, R, and N only, e.g. RRRR.
( ) P elements; these have inverted terminal repeats and move with the help of a transposase enzyme.
( ) Copia elements; these have directly repeated long terminal repeats and move with the help of a reverse transcriptase and an integrase.
( ) F elements; these are long interspersed nuclear elements (LINEs).
( ) Mariner elements; these move via a DNA intermediate.