Complete the non-defining clause about a device: The new monitor, ___, sends an alert when the air becomes unsafe. Use exactly which followed by tracks and the noun phrase indoor air quality, with no added words.
Richtige Antwort
which tracks indoor air quality
Erklärung
Which refers to the monitor, a thing, and supplies the subject of tracks in the inserted clause. Who would also supply a subject, but it would mismatch the nonhuman antecedent.