Scanner and Printer can be made interfaces, then Copier can hold reference to IScanner and IPrinter, it doesn't have to care about their concrete implementation

Scanner and Printer can be made interfaces, then Copier can hold reference to IScanner and IPrinter, it doesn't have to care about their concrete implementations, as long as it's something that has a scan() method and print() method, for all the copier cares it doesn't have to be a powered device at all, it could be a cloud printer and a scanner located 1000 miles away.