177.
B is correct. See the first line: Exploration…appears to have strengthened.”
178.
A is correct as almost every sentence talks about the advantages of optical fibers.
179.
A is correct. See line 6 which states: At present, production costs of optical fibers are relatively high…
180.
D is false as the second last line states:….you need repeaters or boosters every 2 or 3 kilometers (not every 20 kilometers as D states.) All the other answers are true.