Sentence:  Churches can be strengthened through this process of co-optation so long as the environs of the church provide a <WSD>sufficient</WSD> pool of people who can fit the pattern of economic integration ; once the pool of recruits diminishes , the congregation is helpless - friendly contacts no longer keep it going . 
Meaning of the word marked with <WSD> tags:  of a quantity that can fulfill a need or requirement but without being abundant