Which phrase means to work alongside each other?

The phrase "in tandem" signifies working alongside each other harmoniously or cooperatively. It originates from a term describing two horses harnessed together for pulling a carriage, highlighting the idea of collaboration and joint effort. When individuals or teams work in tandem, they synchronize their efforts to achieve a common goal or complete tasks effectively together.

In contrast, the other choices convey different meanings. "In unison" refers to doing something simultaneously or in agreement, while "at odds" suggests a disagreement or conflict, and "in isolation" indicates being separate or alone. These terms do not capture the essence of working together as effectively as "in tandem."