Words that end with the  /t/ or /d/ sounds create an extra syllable when adding -ed to make them past tense

  
-ed	Words that end with a voiced consonant sound - do not change the number of syllables with the added –ed, making only the /d/ sound for the added –ed

-d	Words that end with an unvoiced consonant sound - do not change the number of syllables with the added –ed, making only the /t/ sound for the added -ed
 
-t	
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flooded	 	adapted 	evolved		witnessed  	meditated	ranked
paralleled 	coerced 	structured 	collapsed	fossilized	discriminated 
retained 	compressed	intervened 	scarred 		biased		proportioned
maximized	conveyed 	retrieved 	rotated 	assimilated	mobilized
sequenced 	permeated 	triggered 	receded	oppressed	domesticated
minimized	degraded	vanished 	invoked		ceased 		acquisitioned 
prototyped	exalted		sacrificed	deified 		fortified	suspended 
gutted 		aggravated	diminished	persisted	leased 		annexed
implanted	overlapped 	assessed 	injected		augmented 	prevailed 
seep