Question

Passenger airplanes mostly fly (a)

speeds less than that (b)
sound
1.
Airplanes (C)
_ can fly (d)
greater speeds have been built. This is (e)
if they fly (f)
speeds
greater (g)_
- the speed of sound, (h) fuel consumption increases
enormously.

Answer 1

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

Step-by-step explanation:

We have used at before speed because speed is always countable.

We have used of to show the relation; comparison, between speed of airplanes and sound.

We have used which to clarify that we are talking about planes flying at higher speeds.

We have used because to give the reason.

We have used than to compare the speed of airplanes to the speed of sound.

We have used article the to state a particular thing, fuel consumption increases enormously.

Answer 2

Step-by-step explanation:

Passenger airplanes mostly fly at speeds less than the speed of sound. Airplanes that can fly at greater speeds have been built. This is due to advancements in aviation technology and engineering.

Step-by-step explanation:

a. The phrase "speeds less than that" refers to speeds less than the speed of sound.

b. The speed of sound is a constant speed at which sound travels in a given medium, such as air.

c. The blank space is missing a word, but based on the context, it should be "that."

d. The phrase "can fly" indicates the ability of certain airplanes to reach greater speeds.

e. The sentence is incomplete, and the missing information can vary depending on the context.