Crossword puzzle clue "class level"

Low-level pollution or high-level protection

Warning sign at a train station's food court? (NOTE: The original sign, without my additions, actually exists. It's in Grand Central Terminal in NYC, on the lower level — the food court level. The sig

Management level or theater level

High-level high school science class, briefly

High-level H.S. class with integrals

High-level H.S. class with a lab component