What does the J$-$curve phenomenon refer to in

economics?

$($a$)$ A graphical representation of the relationship

between inflation and unemployment.

$($b$)$ The pattern of a country$’$s CA initially improving

after an appreciation of its currency, then worsening

over time.

$($c$)$ A curve depicting the relationship between interest

rates and investment.

$($d$)$ The fluctuation of a country's GDP growth over time.