(is) by talking ?

[birgit33]

A) "You could improve your accent by talking to native English speakers."
B) "The best way to improve your accent is by talking to native English speakers."

Why does one have to use the verb "to be" (is) in sentence B but not in sentence A?

[bhaisahab]

A) "You could improve your accent by talking to native English speakers."
B) "The best way to improve your accent is by talking to native English speakers."

Why does one have to use the verb "to be" (is) in sentence B but not in sentence A?

Have you tried removing "is" from sentence B and adding it to sentence A? Try it and see if they make sense to you.

[birgit33]

Have you tried removing "is" from sentence B and adding it to sentence A? Try it and see if they make sense to you.

Yes, I've tried it and it doesn't make sense to me.
But I would like to know if the difference (to use or not to use the verb "to be") can be explained grammatically.