Human flea among these are- A: Xenopsylla cheopis B: Pediculus humanus C: Phthirus pubis D: Pulex irritans

中国大学MOOC: Passage 1 Falls are the number one cause of death to old people at home. Most old people can live safely at home if they make a few changes. Falls are common as people are getting older. Up to half of home accidents could be prevented by making some very simple changes. Here are a few suggestions. Mark trouble spots with bright tapes. The first and last steps on stairs are usually high-risk accident are- as. Applying bright tapes and using bright light in these areas would make these spots easier to see. Put grab bars(扶手) in the bathroom. A large number of falls occur in the bathroom. This is unfortunate(不幸的) because its easy to make the area safe from accidents. Putting grab bars in the bathroom gives people something to hang on to. Invest in a personal alarm. A personal alarm can be started if a person falls or otherwise gets in trouble. With the push of a button, the alarm automatically sends a signal, which gets someone to call and see if the person needs help.题目：1. By making some very simple changes at home, old people ______.