The best answer is C. Link aggregation. The requirements point directly to combining multiple physical links into one logical connection. Link aggregation provides higher total bandwidth, supports redundancy if one member link fails, and simplifies administration because the bundle is managed as a single logical interface instead of several separate ones.
Another important clue is vendor interoperability. Standards-based link aggregation, such as LACP, is designed to work across different vendors when supported properly. That makes it a strong match for inter- data-center switch environments where equipment may not all come from the same manufacturer.
The other choices do not satisfy the full requirement list. Spanning tree helps prevent loops, but it can block redundant links instead of actively using them for extra bandwidth. Setting interface speeds to 10GB increases speed per port, but it does not by itself provide the logical bundling, simplified management, or redundancy benefits described. Jumbo frames can improve efficiency for some traffic types, but they are not the right answer for bandwidth aggregation and resilient uplinks.
Because the question asks for a solution that improves throughput, keeps redundancy, remains cost effective, and is easier to manage, link aggregation is the strongest fit.