A two-terminal black box contains one of the R.L.C. elements. The black box is connected to a 220 V AC supply. The current through the source is I. When a capacitance of 0.1 F is inserted in series between the source and the box, the current through the source is 2I. The element is:

• A. resistance
• B. an inductance
• C. a capacitor of 0.5 F
• D. it is not possible to determine the element