单选题 The sales manager was so {{U}}adamant{{/U}} about her idea that it was out of the question for any one to talk her out of it.

【正确答案】 C

【答案解析】划线词adamant“坚硬的，顽固的”。A项adaptable“能适应的，可修改的”；B项anxious“焦急的”；C项firm“坚硬的，坚定的”；D项talkative“多话的”，故应选C项。