Sensei!
All are correct, but I want to discuss ③ "I opened the window only to find the ground covered with snow."
This is correct but it sounds more like written English than spoken English. The spoken English forms would be:
A. "I opened the window only to find the ground was covered with snow."
B. "I opened the window only to find that the ground was covered with snow."
C. "I opened the window only to see the ground was covered with snow."
D. "I opened the window only to see that the ground was covered with snow."
E. "I opened the window, but when I did, I saw that the ground was covered with snow."
E is most common, D is second best, but A, B, and C are also correct.
Sensei, your English is getting better!