In the following question, a short passage is given with one of the lines in the passage missing and represented by a blank. Select the best out of the five answer choices given, to make the passage complete and coherent.

The Centers for Disease Control and Prevention (CDC) is revising its guidelines to acknowledge the spread of the novel coronavirus through aerosols, and to point to inhalation of particles as a common way the virus spreads. A draft of the proposed changes to its recommendations confirmed that airborne particles can spread even by breathing. Moreover, they can remain suspended in air and be inhaled and spread beyond six feet in certain enclosed settings. __________________. In February, researchers from the Wuhan Institute of Virology, in a paper published in Nature, first proposed airborne transmission.