问题：
[单选题]We are in a challenging era of American education, in which demands made on teachers are increasing, _____ adequate retraining is rare.
Asince
Bfurthermore
Cyet
[单选题]We are in a challenging era of American education, in which demands made on teachers are increasing, _____ adequate retraining is rare.
Asince
Bfurthermore
Cyet
