答案是D
agree with sb.------同意某人的观点,建议
agree to sth-------同意对方开出的条件
agree on sth-----同意双方制定的协议条款,合同,协议.
1 Do you agree with me
2 He didn't get the job because he didn't agree to the working conditions here.
3 They agreed on the contract and signed their names.
其实,你的句子最好是：
They agree to go to Spain for their winter holiday this year ----------agree to do sth
语感告诉我,agree to go to Spain- - - - 是正确的表达.