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.2016 was the year that __________ us to look within. Introspection allows us _______________ how invisible forces shape us and how an obsession with trying to establish the pre-eminence of the human brain ______________ us to the intricate connections that we have with bacteria. With a far longer history ____________ people and the unsurpassed masters of survivals, it isn't surprising that there are more bacteria ________________ our guts than there are stars in the Milky Way.With a far longer history ____________ people and the unsurpassed masters of survivals,

• A. than
• B. then
• C. that
• D. when