21. Thank you so much! But for your text message, I ___________ home without my ID card this morning.
A. would have left B. would leave C. had left D. left
22. In English class, our teacher often creates an environment _____________ we are given the opportunity to solve problems ourselves.
A. when B. which C. where D. that
23. John has great singing _____________, but to become a real singer, he needs a lot of necessary training and practice.
A. privilege B. potential C. promotion D. possibility
