Usage of "before long"

[Mr Linguaphile]

Before long, ---- down a half-remembered piece of music ---- as easy as humming the tune.

A) having to track (semanticwise wrong) / was
B) having tracked / would be
C) to track / has been
D) to have tracked / is
E) tracking / will be

Is my analysis OK?

[Alan]

Hi,

That seems fine.

Alan
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English as a Second Language
You can read my ESL story Phrasal Verbs/go