One scenario would involve Giardia having evolved before the origin of mitochondria--it would never have had them. Other primitive eukaryotic features would be expected to be present if this were true. Another scenario would see Giardia having lost mitochondria for some reason during its evolutionary history. In this case, Giardia would have appeared after the origin of mitochondria.
Work Step by Step
If something does not possess a feature, it either never had it or has lost it. From there, to answer the question, you just have to construct scenarios based on those two possibilities.