Which of the Following Is the Best Definition of Synergy

Which of the following is the best definition of synergy?

A) Combinations of firms that have been joined by merger, consolidation, or acquisition.
B) A public offer by one firm to directly buy the shares from another firm.
C) The positive incremental net gain associated with the combination of two firms through a merger or acquisition.
D) Agreement between firms to cooperate in pursuit of a joint goal.
E) Corporate takeover bid communicated to the shareholders through a stock exchange.