Before Entering a Confined Space to Do a 3 to 5

Before entering a confined space to do a 3 to 5 minute valve replacement, samples are taken of the air inside. The following data is known about the gases present: TLV = 100 ppm
LFL = 500 ppm
UFL = 2000 ppm
Actual concentration measured = 2100 ppm
What would be considered a safe concentration?

A) Below 50 ppm
B) Below 100 ppm
C) Below 500 ppm
D) Above 2000 ppm
E) Above 2100 ppm