'Exercise' is a reqular noun. Look at the verb exercise. It has a consonant and a silent e at the end, so just add d to the end of the base form of the verb exercise. Then you can make the past tence. Exercised is pronounced [..zd]. As s[es] is pronounced [z],you should say [...zd]. The z sound is a voiced sound, so ed should be pronounced as a voiced sound d.
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Thank you for your help. This is the explanation about how to make the past tence. Is my explanation above grammatical?
