Read the list of sentences from the article.
1. Like inactivity, space flight leads to the loss of both strength and skeletal muscle mass, in a process known as atrophy.
2. During long spaceflights on the ISS, research found that 37 crew members experienced a decrease in average strength of between 8 and 17 percent.
3. They make the new material they need or get rid of any material that isn't needed.
4. During spaceflight, however, the balance of these two processes changes, which leads to reduced bone mineral.
Which two sentences taken together provide the BEST explanation for WHY the body loses muscle and bone mass while in space?
