Directions:
Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C or D on the ANSWER SHEET. (10 points)
　　Today, we live in a world where GPS systems, digital maps, and other navigation apps are available on our smartphones. (1) _____ of us just walk straight into the woods without a phone. But phones (2) _____ on batteries, and batteries can die faster than we realize. (3) _____ you get lost without a phone or a compass, and you (4) _____ can't find north, a few tricks may help you navigate (5) _____ to civilization, one of which is to follow the land.
　　When you find yourself well (6) _____ a trail, but not in a completely (7) _____ area, you have to answer two questions: Which (8) _____ is downhill, in this particular area? And where is the nearest water source? Humans overwhelmingly live in valleys, and on supplies of fresh water. (9) _____, if you head downhill, and follow any H2O you find, you should (10) _____ see signs of people.
　　If you've explored the area before, keep an eye out for familiar sights—you may be (11) _____ how quickly identifying a distinctive rock or tree can restore your bearings.
　　Another (12) _____: Climb high and look for signs of human habitation. (13) _____, even in dense forest, you should be able to (14) _____ gaps in the tree line due to roads, train tracks, and other paths people carve (15) _____ the woods. Head toward these (16) _____ to find a way out. At night, scan the horizon for (17) _____ light sources, such as fires and streetlights, then walk toward the glow of light pollution.
　　(18) _____, assuming you're lost in an area humans tend to frequent, look for the (19) _____ we leave on the landscape. Trail blazes, tire tracks, and other features can (20) _____ you to civilization. 

A.Since

B.If

C.Though

D.Until