$.$ Suppose, in the North, one unit of labor produces fn units of fish or cn units of chips. In

the South, one unit of labor produces fs units of fish and cs units of chips. For the South to

specialize in fish, which of the following must be true?

$($a$)$ fx $>$ cs

$($b$)$ fs

cs $>$ fn

cn

$($c$)$ cs

fs $<$ cn

fn

$($d$)$ fs

cs $<$ fn

cn

$($e$)$ fscs $<$ fnc