"Which of the following is evidence that mitochondria have an endosymbiotic origin? A. They contain their own DNA B. They produce ATP C. They are enclosed by a membrane D. Mitochondrial diseases are maternally inherited"

A. They contain their own DNA

Explanation:

Mitochondria is a eukaryotic cellular organelle which is thought to be evolved by the symbiotic relationship between the prokaryotes and the proto-eukaryotes.

The mitochondria were once a free-living prokaryote which during the course of evolution was engulfed by the proto-eukaryote. They formed the symbiotic relationship with each other and the prokaryote evolved into the mitochondria.

There are many pieces of evidence which suggest the endosymbiotic hypothesis one of which is provided in the option is that they contain their own DNA just like the prokaryotes that is one circular DNA present in their cytoplasm not enclosed by the  

Thus, Option-A is correct.