Dovetail /ˈdʌv.teɪl/ (first syllable stressed)

Stress Patterns of the Options:

• A. proviso /prəˈvaɪ.zəʊ/ (second syllable stressed) 
• B. simplicity /sɪmˈplɪ.sɪ.ti/ (second syllable stressed) 
• C. jargon /ˈdʒɑː.ɡən/ (first syllable stressed) 
• D. psychiatry /saɪˈkaɪ.ə.tri/ (second syllable stressed) 

Since "jargon" has the same first-syllable stress as "dovetail," the correct answer is C. jargon.