Which one of the following words is similar in meaning to the word, 'readily' (Para 1) as used in the passage?

'Readily admit' in the context means to admit frankly or openly without hesitation. 'Frankly' best captures this sense of candidness. 'Easily' suggests lack of difficulty, 'efficiently' relates to manner of doing work, and 'plainly' means clearly—none capture the openness/willingness implied by 'readily admit'.