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Answer:
AD is the diameter
Step-by-step explanation:
Angles in a triangle have a sum of 180°, so inscribed angle B is 80° and inscribed angle E is 90°.
An inscribed angle subtends an arc that is twice its measure, so arcs ABD and AED are both 180°. That makes chord AD a diameter.
Points A and D need your cross markings. AD is a diameter of the circle.