What is the purpose of "backpressure" mechanisms in a streaming data pipeline, and what can happen if they are absent?

A Backpressure signals upstream producers to slow down when downstream consumers can't keep up; without it, queues can grow unbounded, leading to memory exhaustion or dropped data B Backpressure guarantees that producers will always speed up regardless of consumer capacity C Backpressure is a feature that only applies to batch processing, never streaming D Without backpressure, systems automatically scale infinitely with zero resource constraints