Ask which option is about processes competing for shared access. Thrashing and demand paging both belong to memory management, so they are out. The convoy effect is a scheduling artifact of FCFS, not a synchronization bug.
Starvation is the case where a waiting process is repeatedly passed over and never granted the resource it needs. That is a direct outcome of unfair or improper synchronization among processes.
\[\boxed{\text{Starvation}}\]