The correct answer is D. Society must look after the poor.
A. Society must have looked after the poor is incorrect because it uses the past tense, which implies that society has already taken care of the poor. However, this is not the case. The poor are still in need of help, and society must continue to look after them.
B. Society must be looked after the poor is incorrect because it uses the passive voice, which makes it sound like the poor are helpless and need to be taken care of by others. However, the poor are not helpless. They are capable of taking care of themselves, and society should provide them with the resources they need to do so.
C. Society must looked after the poor is incorrect because it is grammatically incorrect. The correct verb form is “look after.”
D. Society must look after the poor is the correct answer because it uses the active voice and the present tense. This implies that society is taking action to help the poor and will continue to do so in the future.