The question asks for a word similar in meaning to QUELL, which means to suppress, subdue, or put an end to something. 'Stifle' means to suppress or restrain, which is the closest synonym. The other options ('Blatant', 'Howling', 'Clamorous') all relate to noise or being obvious, which are unrelated to the meaning of quell. To quell something is to stifle it.