An electroscope is a device that detects charge on objects that touch it or are brought near it. John rubs a piece of cotton fabric on a plastic rod and then touches the rod to the electroscope.

Rubbing the cotton fabric against the plastic rod transfers electrons between them, charging the rod by friction. When John touches the charged rod to the electroscope, charge is transferred through direct contact, which is conduction. Therefore, the rod is charged through friction and the electroscope through conduction: choice D.

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