Read the sentence below.

He said it was faster than trying to decode my texts, I didn't understand
what he meant until a few days later.

What is the correct way to write this sentence?

A He said it was faster than trying to decode my texts, but I didn't
understand what he meant until a few days later.

B He said it was faster than trying to decode my texts: I didn't
understand what he meant until a few days later.

C He said it was faster than trying to decode my texts. Which I didn't
understand what he meant until a few days later.

D He said it was faster than trying to decode my texts, and I didn't
understand. What he meant until a few days later.