Ozone occurs both in the Earth's upper atmosphere and at ground level. Ozone is a gas composed of three atoms of oxygen. Ground-level ozone, the topic of this website, is “bad” because it can trigger a variety of health problems, particularly for children, the elderly, and people of all ages who have lung diseases such as asthma. Stratospheric ozone is “good” because it protects living things from ultraviolet radiation from the sun. Therefore, you have to think about the time the action happens before applying either had done or have done.Ozone can be “good” or “bad” for health and the environment depending on where it’s found in the atmosphere. Had done can be used with any pronoun without a problem.For the third person singular pronouns such as he and she, you have to use has done. Have done can be used only with first person and second person pronouns as well as third person plural form.Had done is used to speak about an action that was completed a long time ago in the past.If we know the time, the tense changes to simple past. ![]() This can be recent past where we do not know the exact time when the action took place.
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