Which of the following are most suitable indicators of SO₂ pollution in the environment?

A lichen is a symbiotic organism composed of a fungus and an alga. Lichens are highly sensitive to changes in their environment, particularly air quality. SO₂ pollution in the atmosphere can affect lichens in several ways, including by reducing their growth and survival rates, and altering their morphology and physiology. Therefore,
monitoring the health and abundance of lichens in an area can be a useful indicator of SO₂ pollution.
(1) Algae are not as sensitive to SO₂ pollution as lichens.
(2) Fungi are not as sensitive to SO₂ pollution as lichens.
(4) Conifers may show symptoms of SO₂ pollution, but they are not as reliable indicators as lichens.