In the absence of external force acting n a rigid system, which of the following must remain constant 1) angular momentum 2) linear momentum 3) moment of inertia 4) kinetic energy Which one is the correct answer ?

Question

$a)\; 1\; and\; 2\\b)\; 2\; and\; 4 \\c)\;3 \;and\; 4 \\d)\; 1\; and\; 4$