Final answer:
The true statement about signing the number 'twenty-one' is that you will sign 'two' followed by 'one.' This does not involve bending the thumb, wiggling the middle finger, or using a bounce motion.
Step-by-step explanation:
The statement that is true about signing the number "twenty-one" is that you will sign 'two' followed by 'one.' In American Sign Language (ASL), numbers are signed with specific hand movements and positions that correspond to each number. When signing the number twenty-one, the signer first makes the handshape for the number 'two' then changes to the handshape for the number 'one.' It does not involve bending the thumb up and down or using a bounce motion. There is no wiggling of the middle finger but a simple transition from the sign for 'two' to the sign for 'one.'