—You should have thanked the hostess before leaving. —I meant . But I couldn’t find her w

—You should have thanked the hostess before leaving.
—I meant . But I couldn’t find her when I was leaving.
A. to
B. to do
C. doing
D. doing so

(答案→)A. toB. to doC. doingD. doing so解析：这题考察不定式的省略式，完整的说法是：I meant to thank the hostess before leaving。因为上文已有了动词，下文就要省略，保留to。句意是：--你本应该离开前感谢女主人的，--我本来打算的，但我离开时找不到她。选A。

就是这个解释