全部

1·All are radioactive and have similar properties to actinium.

这些元素都有放射性，而且性质与锕相似。

2·There are three naturally occurring radioactive series - the thorium series, the actinium series, and the uranium series.

有三个天然存在的放射系列，即钍系、锕系和铀系。

锕

1·All are radioactive and have similar properties to actinium.

这些元素都有放射性，而且性质与锕相似。