The Mass is the fixed value. It doesn’t change by changing its shape ?

The center of mass doesn't move from one part of the raft to the other, but the raft moves from one side of the center of mass to the other. The raft is not fixed, from the perspective of the lake. As the boy's feet push himself forward, they also push the raft backward.

Explanation:

i take the test and it's correct

i might be wrong but i think its a. let me know if i’m right and have a good rest of your day!