$34\mathrm{.}10.$MANK$09$

benevolent social planner would prefer that the output of good $x$ be increased from its current level if$,$ at the current level of output of good $x,$

a$.$ social value $=$ private cost $=$ social cost $>$ private value.

b$.$ social value $=$ private value $=$ private cost $$ social cost.

c$.$ social cost $=$ private cost $=$ private value $$ social value.

d$.$ social cost $>$ private value $=$ social value $>$ private cost.