211.About six years ago I was eating lunch in a restaurant in New York City vrrhen a woman and a young boy sat down at the next table;I couldn't help overhearing parts of their conversation.
本句包含两个分句。前一个分句的主干是I was eating lunch，其前的About six years ago是介词短语作状语，其后的when a woman and a young boy sat down at the next table为状语从句。后一个分句的主干是I couldn't help overhearing parts。
couldn't help doing是个固定表达，意为“禁不住做某事，情不自禁地做某事”。如:
She couldn't help smiling.她禁不住笑了起来。
I happened to overhear what he said.我碰巧听到他说的话。