[A] conscious [B] consciously [C] unconscious [D] unconsciously
Although eyewitnesses to the phenomenon report that they did not see anything in the sky that could account (44) the ice, scientists had to come up with a rationalization. Professor Jesus Martinez Frias, the geologist investigating the ice falls in Spain, told BBC News that the ice pieces had probably been (45) through sudden temperature drops in the stratosphere. This was the most likely explanation, he said, for the "very unusual" phenomenon.