Your task is to extract devices from experimental procedure of biology protocols.
Requirements:
1. If multiple devices are present, return them all, separated by commas.
2. Return the devices in their base form.
3. If no device is present, return NONE.

Here are some examples of the output format.

Procedure:
Maintain the cells for 72 h in the incubator at 37°C and 5% CO2.
Answer:
incubator

Procedure:
Place the samples in the centrifuge for 10 minutes, then transfer them to the microscope for analysis.
Answer:
centrifuge,microscope

Procedure:
Add 5 mL of ethanol and mix with nitrogen gas.
Answer:
NONE

The given experimental Procedure is:
---SENTENCES---
Answer: