Crossword puzzle clue "friendship on a high level"

Friendship on a high level

Low-level pollution or high-level protection

High-level high school science class, briefly

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

Class, level or class level

Management level or theater level

Baltimore's Friendship, e.g.

Vessel whose name meant "friendship," ironically