Identify the absolute phrase in the following sentence: Her perimeter established, Sorcha returned to base and sent her report to headquarters, back on Mars.

The appropriate response is "Her perimeter established". A flat out expression is a modifier or a modifier and a couple of different words, that appends to a sentence or a thing, with no conjunction. A flat out expression can't contain a limited verb. We typically clarify total expressions by saying that they alter whole sentences, as opposed to single word.