What years from the 1900s and 1800s are the same year when read upside down?

What are these words or phrases, which contain the word cat?

A dreadful event (11 letters)
A robber who climbs walls (10 letters, 2 words)
A systematic list (7 letters)

Fill in the blanks:

U N D _ _ _ _ _ U N D

A woman gave a man a list of things she needed to buy at the store. The man gave the list back to the woman and she turned red with embarrassment. Why?

When can ten plus ten equal ten, yet ten minus ten equal twenty?