问题补充：
When Peter the car door, he found the key left in his car. So he had to call for help.
A. opened
B. was opening
C. was to open
D. had opened
答案：
A. opened
B. was opening
(答案→)C. was to open
D. had opened
解析：句意：当皮特刚想打开门时，发现钥匙忘在了车里，因此他不得不求助。因为皮特他没有钥匙，想打开门还未打时，表将来，只有be to do 可以表将来，故选C。
