Wikipedia lists eight units of radioactivity, including the curie, the rutherford and the sievert (as well as the bequerel).
The becquerel is the SI unit of radioactivity. The curie and the rutherford are similar units in other measuring systems; the sievert is an SI unit – "a measure of the health effect of low levels of ionizing radiation on the human body."
The SI system also includes the gray, which is defined as "the absorption of one joule of radiation energy per kilogram of matter." I suppose you could argue that this is not actually radioactivity, and for that matter you could probably say the same about the sievert.
Even so ... question setters should always remember to specify the SI system when asking about units (if that's what they're referring to). But in this case there would appear to be at least one other SI unit that fits. This question would have been better asked the other way round.
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