Ah, thank you. Your post said:
At trial, the Fifth Amendment gives a criminal defendant the right not to testify. This means that the prosecutor, the judge, and even the defendants own lawyer cannot force the defendant to take the witness stand against his or her will. However, a defendant who does choose to testify cannot choose to answer some questions but not others. Once the defendant takes the witness stand, this particular Fifth Amendment right is considered waived throughout the trial. - See more at: Fifth Amendment Right Against Self-Incrimination - FindLaw
Unfortunately, this contains several inaccurate statements.
"At trial, the Fifth Amendment gives a criminal defendant the right not to testify."
No, it gives them the right to not incriminate themselves. The right to refuse to answer any question(s) where he feels the answer might incriminate him.
But the person (or his lawyer) must appear in court and state that the person refuses to answer on that grounds.
The 5th amendment neither says nor means anything of the kind. It says (and means) that the person cannot be forced to incriminate himself. But he (or his lawyer) can be compelled to state something like, "I decline to answer, as is my right under the 5th amendment, because the answer might incriminate me."
"However, a defendant who does choose to testify cannot choose to answer some questions but not others."
The 5th doesn't say anything like that. It simply says he cannot be compelled to testify against himself. It does not say anything like "unless he starts to testify and then decides to stop, then he CAN be compelled..."
"Once the defendant takes the witness stand, this particular Fifth Amendment right is considered waived throughout the trial."
Again, the 5th amendment doesn't say this at all. See my comments above.
I suggest you read the Constitution to find out what the Constitution says. You'll find it quite direct and clear, especially in this case. (And it's also the Supreme Law of the Land.) Don't bother reading what someone else
claims the Constitution says. As I have shown here, they can be very wrong... and definitely are in this case.