Drones -1- in a similar way to helicopters and airplanes. When the engine is turned on, the propellers start to spin. This helps the drone ---2---. Once it's up there, a pilot on the---3--- uses a remote control to guide the drone - --4--- Its flight. Every drone has a "central flight controller" responsible for 5 stability. You can think of it like a compass. Most drones ---6--- with four propellers but some can three, six, or even eight propellers. ---7- -- propeller usually has two blades to help the drone stay steady when It's flying. To make this happen, two of the propellers spin in one direction 8--- the others spin the opposite way.
1. (A) works (B) work (C) will work (D) worked 2. (A) takes off (B) to take off (C) taking off (D) taken off 3. (A) land (B) soil (C) ground (D) floor 4. (A) while (B) during (C) when (D) just 5. (A) maintain (B) to maintain (C) maintaining (D) to maintaining 6. (A) are equipped (B) are equipping (C) equips (D) equip 7. (A) Each (B) All (C) This (D) These 8. (A) besides (B) however (C) though (D) while ---​