Difference beetween those two forms

[Tom]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #99 "The Parliamentary Candidate (2)", question 1

Henry: Hello.
Man's voice: Is that Mr. Henry Orpington, the parliamentary candidate?
Henry: Yes, ..........

(a) talking
(b) dictating
(c) speaking
(d) deciding

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #99 "The Parliamentary Candidate (2)", answer 1

Henry: Hello.
Man's voice: Is that Mr. Henry Orpington, the parliamentary candidate?
Henry: Yes, speaking.

Correct answer: (c) speaking
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Hi!
What's the difference beetween those two forms?
Are they both correct?
When do we use them and which one is more popular or proper?

Thanks,
Tom

[Mister Micawber]

.
Which two forms? Only speaking is correct, among the choices given. It is a set phrase.

.
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Native English teacher at Mister Micawber's

[tommy]

Sorry, I wrote it by mistake.