Explanation

(c)
Slow acting nitrogenous fertilizer is one which decomposes slowly. out of given choices CaNCN (or $CaCN_{2}$ or calcium cyanamide)decomposes very slowly.
CaNCN+2H_{2}O ⟶ CaCO_{3}+NH_{2}CONH_{2}
_{urea}
NH_{2}CONH_{2}+ H_{2}O ⟶ CO_{2}+NH_{3}
$NH_{3}\overset{Nitrifying\ bacteria}{\rightarrow}\ Soluble\ nitrates \rightarrow plants$