Anthony is learning about electric circuits. he has started building a circuit shown below. which of the following items should he add to his circuit to test wether it has a current flowing through

Since you haven't added neither the circuit nor the choices, I cannot give you a precise choice.
However, I can tell you how to detect current in the circuit.

A current in the circuit can be detected and measured using a device known as ammeter.
Ammeter is connected in series with the path of the current to be detected/ measured.
If the ammeter reads zero values, this means that no current is flowing in the circuit.
If the ammeter detects a value, this means that current is flowing in the circuit.

they lose energy. because of that, they slow down and get closer together