What is the best method to ensure the parameters are passed successfully to the data upsert page?

A developer is creating a CloudPage which accepts secure parameters via an email link and will submit those parameters to another CloudPage for data upsert. The page currently captures an Appointment ID parameter passed into it and sets the value to the variable caapptld. The developer does NOT want the Appointment ID to be visible to anyone using the form.

What is the best method to ensure the parameters are passed successfully to the data upsert page?
A . <input id="apptld" type="textarea" value»"%%«v(@>apptld)»%%" readonly>
B. <form action="%%=MicrositeURL(123,,apptId",@apptId)a%%" method="post">
C. <form action«"%%»CloudPagesURL(123,’apptId’,@apptId)«%%" methods "post">
D. <lnput ld=MapptId" type="textarea" value="%%«v(@apptld)«%%" hldden>

Answer: C