Answer:
D. Schools should move away from standardized testing because tests often do more harm than good.
Explanation:
Claim D is focused on testing in schools and is, therefore, the narrowest of all.
Claim A seems to be focused on hydraulic fracturing and how harmless it is, yet it also mentions natural gas as an important byproduct.
Claim B is about inadequate zoo habitats for two different species of animals, so it cannot be considered the narrowest and most focused claim.
Claim C seems to be focused on cutting welfare programs, yet it also mentions the problem of homelessness among veterans. Not the narrowest claim either.