I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries. Hydrogen is an authorized food additive (E 949) that allows food package leak testing among other anti-oxidizing properties."? 

What is not an application for hydrogen: aerospace, telecommunications, or pure?