The four sentences (labelled $1,2,3,4$) below, when properly sequenced would yield a coherent paragraph. Decide on the proper sequencing of the order of the sentences and key in the sequence of the four numbers as your answer:
- But the attention of the layman, not surprisingly, has been captured by the atom bomb, although there is at least a chance that it may never be used again.
- Of all the changes introduced by man into the household of nature, [controlled] large-scale nuclear fission is undoubtedly the most dangerous and most profound.
- The danger to humanity created by the so-called peaceful uses of atomic energy may, however, be much greater.
- The resultant ionizing radiation has become the most serious agent of pollution of the environment and the greatest threat to man’s survival on earth.