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.

Consciousness resembles a stream also in other particulars. A stream is __________ unbroken whole from its source to its mouth, and an observer stationed at one point cannot see all __________ it at once. He sees but the one little section which _____________ to be passing his station point at the time. The current may look much the same from moment to moment, but the component particles which constitute the stream are _________________ changing. So it is with our thought. Its stream is continuous from birth till death, _____________ we cannot see any considerable portion of it at one time.