(is) by talking ?

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?

In (A) ‘improve’ is the main verb.

In (B) ‘to improve’ is not the main verb, so a main verb is required.

In (A) ‘improve’ is the main verb.

In (B) ‘to improve’ is not the main verb, so a main verb is required.

Terrific!

kind regards,

“The best way to improve your accent” ~ subject.
“is” ~ copula.
“talking/talk/to talk to NES” ~ subject complement.

“by” should be thrown out from the sentence.

Am I right or wrong? Thanks

It’s an interesting question. “By talking to native English speakers is the best way to improve your accent” is wrong (“by” should be deleted), and yet the other way round it sounds OK. It may be a case of something logically imperfect being used so often that it becomes de facto correct.