Her eyesight was acute.

Vacillate most nearly means

Some pollutants that render air unsafe to breathe cannot be seen or smelted. Nitric oxide, carbon monoxide, and radon gas are examples. Other pollutants, such as formaldehyde, can be smelted at high levels only but are still unsafe to breathe even at lower levels.
You can conclude from the paragraph that formaldehyde

This subject almost exceeds my comprehension

Opposition to current flow is measured in