Static Electricity - Mission SE5 Detailed Help

Two neutral conducting pop cans are touching each other. A negatively charged balloon is brought near one of the cans. The cans are separated while the balloon is nearby. After the balloon is removed the cans are charged. The cans were charged by the method of ____.
Methods of Charging:
There are three methods of charging that are commonly discussed in a static electricity unit - charging by friction, charging by conduction (or contact), and charging by induction.

Triboelectric charging (Charging by friction) usually involves the rubbing of two objects together.

Charging by conduction (or contact) involves the touching of a charged object to a neutral object.

Charging by induction involves bringing a charged object near to but not touching a neutral object in order to polarize the object and then charging it by momentarily connecting it to a ground.