Safe haven for transposon is described as a site in the genome where the insertion of a transposable element does not cause a mutation. Insertion of a transposon into a safe haven prevents harm to the host and the transposon survives (it will be successfully inherited).
Introns are regions of genome which do not code for a protein. Similarly, transposable elements are generally not essential for survival of a cell. These two are considered as safe havens for transposable element insertion as the insertion does not harm the cell.
Since insertion of a transposon in an intron or other transposable elements does not harm the cell, options (a) and (b) are true. Thus, the correct answer is option (d) a and c are both correct
Exons are coding regions of genome. Insertion of a transposon into these regions disrupts the gene, causes loss of a vital function, and may lead to cell death. Due to this, exons are not considered as safe havens for transposons. Hence, option (b) exons is not correct