I think the answer is c. Sentence 3
Sorry if wrong
<em>How it works. </em><em>A camera obscura is a dark room with a small hole in one wall in its simplest form.</em><em> When it's bright outside, light enters through the hole and projects an upside-down image of the outside world onto the wall opposite the hole.</em>
Neil Armstrong walked on the ROCKY moon in 1969
The answer is B)<span>Walking is an easy and safe exercise for beginners. The paragraph is explaining that walking doesn't need much fancy equipment and that it is something easy for beginners.</span>