Glacial erosion is a very important process shaping Yosemite’s landscape. Hanging valleys are a glacial feature that develops where:

waterfalls

Explanation:

Waterfalls are the most common places were the hanging valleys occur and such generally form when the ice erodes the main chunks of rocks that leaves the tributary valleys hanging above the main valley floor.This  takes places after the glaciers have melted and eroded away. Thus Yosemite park is best known for waterfalls.

A,) cause a & b are equal & both gives 180°