Answer:
siRNA.
Step-by-step explanation:
The RNA interference may be defined as the evolutionary conserved mechanism that helps in the gene regulation by the silencing of the small RNA molecules. Two main types are siRNA and miRNA.
The siRNA (small interference RNA) is involved in the protection of the cell by destroying the exogenous ds DNA of the cell. The DICER enzyme plays an important role in the processing of the small interference RNA and the guide strand of RNA is involved in the gene silencing.
Thus, the answer is option (a).