It’s a curiously worded question. Ionizing radiation is that which is typically seen as most damaging to life causing “radiation sickness” and of the three forms, alpha and beta particles are less damaging than gamma rays when outside the human body and are both more easily blocked whereas gamma rays are most penetrating and likely to be lethal. The question talks about being absorbed by the tissue which may be a significant emphasis, I don’t know. If it means something that could be inhaled or injested then it is possibly restricting the answer to just alpha or beta particles and of the two beta is seen as more harmful typically. However on balance I think the question is referring to gamma rays.
