Final answer:
The guardian's understanding of car seat use is indicated by their statement: "I should secure the car seat using lower anchors and tethers instead of the seatbelt."
Step-by-step explanation:
The statement that indicates an understanding of car seat use is:
A) I should secure the car seat using lower anchors and tethers instead of the seatbelt.
Using the lower anchors and tethers is the recommended method to secure a car seat as it provides a secure attachment to the vehicle. This method is safer than using the seatbelt alone, which can be less secure and may lead to improper installation of the car seat.