Silicon Has Often Been Suggested as an Alternative to Carbon

Silicon has often been suggested as an alternative to carbon in biochemistry. Each of the following is one reason silicon is unsuitable for such a role EXCEPT ONE. Which is the EXCEPTION?

A) Silicon compounds are too soft or too hard to be part of living organisms.
B) Silicon compounds react too much or too little to be part of living organisms.
C) Silicon atoms bond with up to four other atoms.
D) Silicon compounds react too slowly to undergo the rapid changes required of molecules in organisms.