Doctor's orders

Question: One day a man broke his leg. When he was sent home from the hospital he had to use a wheelchair. The doctors told him he could not go up stairs. When the man got home he realized he had stairs to get into his house on both sides. The man saw his neighbor, the doctor who x-rayed him at the hospital, getting out or her car. The man asked "can you carry me up the stairs?" The woman replied "no." Why?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: What can be broken but never forgotten?

Question: Which thing that comes once in a year, twice in a week?

Question: You are trying to get your chicken, fox, and wheat to the barn. However, the barn is on the other side of the river. You are on a boat and can only transport one animal or wheat at a time. You must choose carefully not to leave the wrong two together, though. It's either the fox will eat the chicken or the chicken will eat the wheat. How do you take each thing across safely?

Question: During what month do people sleep the least?