Answer: Choice D
ST = SE or US = FS
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Step-by-step explanation:
As you mentioned, HL stands for hypotenuse leg. The sides EF and UT marked with triple tickmarks are congruent, and they are the congruent hypotenuses. That takes care of the "H" part of "HL". So we can cross off choice C because it mentions TU = EF, which is already taken care of.
The "L" part can involve either leg of the triangles. So we could involve the legs ST and SE (they appear to be the shorter legs), or we could involve the longer legs US and FS. We only need to pick one of those options to handle the "L" portion. If we knew all three aspects, then we could easily refer to the SSS (side side side) congruence theorem.
The HL theorem only applies to right triangles.