Question

Passenger airplanes mostly fly (a) _______ ( on / at / in / for) speeds less than that (b) _______ ( at / in / of /on) sound. Airplanes (c) ___________ (who / when / what / which) can fly (d) _______ (at / in / of /on)

greater speeds have been built. This is (e) ____________ (when / why / as / because) if they fly (f) _______

(for / from / in / at) speeds greater (g) ___________ (then / than / of / as) the speed of sound, (h) _______

(a / an / the / that) fuel consumption increases enormously​

Answer 1

Answer:

Passenger airplanes mostly fly at speeds less than that of sound. Airplanes which can fly at greater speeds have been built. This is because if they fly at speeds greater than sound, the fuel consumption increases enormously.

Answer 2

Answer:

Passenger airplanes mostly fly at speeds less than that of sound. Airplanes which can fly at greater speeds have been built. This is because if they fly at speeds greater than the speed of sound, the fuel consumption increases enormously.

Explanation:

1. We have used at before speed because speed is always countable.
2. We have used of to show the relation; comparison, between speed of airplanes and sound.
3. We have used which to clarify that we are talking about planes flying at higher speeds.
4. We have used because to give the reason.
5. We have used than to compare the speed of airplanes to the speed of sound.
6. We have used article the to state a particular thing, fuel consumption increases enormously.