must thunder
Regular verb: thunder - thundered- thundered

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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it must thunder
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it must be thundering
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it must have thundered
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it must have been thundering
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Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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it mustn't thunder
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it mustn't be thundering
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it mustn't have thundered
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it mustn't have been thundering
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Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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must it thunder?
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must it be thundering?
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must it have thundered?
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must it have been thundering?
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Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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mustn't it thunder?
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mustn't it be thundering?
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mustn't it have thundered?
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mustn't it have been thundering?
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