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.
According to some philosophers, thinking philosophically is not the same as thinking ________ Philosophers have a passionate ________ for analytical thinking. On the other hand, most ordinary people do ________ have a passionate curiosity when it comes to thinking. What they want is to think logically and arrive at a solution. ________ this sense, you do not have to be a philosopher to think philosophically. However, ________ you are grappling with a problem of great magnitude, you have to think philosophically.

However, ________ you are grappling

1. A
   hence
2. B
   if
3. C
   so
4. D
   then