Sustuning or Sustaining: How To spell?

The word Sustuning is misspelled against Sustaining, which is present continuous of "Sustain"

Word contains consecutive vowels 'AI' in between alphabets sust & ning is misspelled as 'U'
Wrong Spelling:  sust-u-ning 
Correct Spelling:  sust-ai-ning 
Check more misspelled words of Sustaining to spell it correct.

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