Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: Clear mucus is secreted before ejaculation to neutralize acidic urine remaining in the urethra.

Answer: What is secreted before ejaculation to neutralize acidic urine remaining in the urethra?


Question: Molar masses can be used to determine the mass of a quantity of material.

Answer: What can be used to determine the mass of a quantity of material?


Question: The esophagus runs a mainly straight route through the mediastinum of thorax.

Answer:
The esophagus runs a mainly straight route through the mediastinum of what?