In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.
Passage:

We all experience and understand that the current times are not very safe in general. One has to be on a ______ guard against unfriendly elements. As we move towards the Golden Age on the planet, a ______ of negative forces have surfaced. It is by bringing them to the surface that the divine forces can put them to an end. It is like the ______ that surfaces when we boil sugar in water, which is ready to be removed from the top so that what we get is sugar solution ______ of all the impurities. This process of cleansing our planet by the universal forces, however, will take some time. Till then, we have to ______ these negativities around us.