Internal forces can change

Under which force the centre of mass is moving?

Choose the correct statement$(s)$:
$(A)$ The position of the centre of mass of a system is dependent on the choice of coordinate system.
$(B)$ Newton's second law of motion is applicable to the centre of mass of the system.
$(C)$ Internal forces cannot change the state of the centre of mass.
$(D)$ Internal forces can change the state of the centre of mass.

$A$ monkey of mass $m$ is at rest on a light rope attached to a balloon of mass $M$ in mid-air. If the monkey climbs up the rope and reaches the top of the rope,what is the distance covered by the balloon? (The total length of the rope is $L$)

If a force $10 \hat{i} + 15 \hat{j} + 25 \hat{k}$ acts on a system and gives an acceleration $2 \hat{i} + 3 \hat{j} - 5 \hat{k}$ to the centre of mass of the system,the mass of the system is

The multiplication of the total mass of a system and the acceleration of its centre of mass denotes what?