which one is correct??

[reza_otiz]

I am confused with this structure, about comparative adjective..

1. Goddard developed the first rocket to fly faster than sound is.
2. Goddard developed the first rocket to fly faster than sound does.
3. Goddard developed the first rocket to fly faster than sound.

 

[5jj]

#1 is incorrect; #2 is possible. #3 is what we normally say.

 

[Rover_KE]

Welcome to the forum, reza_otis. :hi:

Note that a better title would have been Faster than sound, as that is what your question is about.

Rover