I may be digressing here...Does the word "outgrowth
" have a plural? Is "outgrowths
" really a plural of outgrowth
IMO, outgrowth has no plural
Refer to Webster dictionary - it gives no plural form for word outgrowth http://220.127.116.11/dictionary/outgrowth
In that case shouldn't (b) be the answer?
Outgrowth has a plural form. Try googling "outgrowths" and you will find plenty of scientific texts that utilize it. B cannot be a right answer. "A coolness of judgment and mutability of purpose" call for a plural noun.