The oxygen level today is maintained at around 20 per cent by plants and bacteria that produce oxygen gas as a by-product of photosynthesis.
(The oxygen level today; is maintained; L:at around 20 per cent; by plants and bacteria) (plants and bacteria; produce; oxygen gas; as a by-product of photosynthesis)
The oxygen level today plants and bacteria
is maintained produce
L:at around 20 per cent by plants and bacteria
oxygen gas as a by-product of photosynthesis