Which of the following does not explain why radioactive strontium is used in treating bone cancer?

Radioactive strontium is similar to calcium which is a component of bones, so it is also absorbed by normal bone cells and cancer cells.

Radioactive strontium emits beta radiation that kills cancer cells or slows their growth by damaging their DNA.

Radioactive calcium is rarely found.

Radioactive strontium undergoes beta decay which irradiates bone marrow cells.