Answer: Job

The Spark execution hierarchy from coarsest to finest is: Job → Stage → Task. A **Job** is triggered by an action (e.g., `count()`, `save()`) and represents the highest-level unit of work. A Job is divided into **Stages**, separated by shuffle boundaries (e.g., due to wide transformations like `groupBy()`). Each Stage consists of **Tasks**, which are the smallest units of work and operate on data partitions. **Executor** and **Slot** relate to resource allocation, not the logical execution hierarchy. Thus, the coarsest level is **Job** (B).

Author: LeetQuiz Editorial Team