So CACTUS, FOCUS and  RADIUS become CACTI, FOCI and RADII - although, the standard English FOCUSES sounds a lot  less poncey than FOCI.

因此 CACTUS、FOCUS 和 RADIUS 变成 CACTI、FOCI 和 RADII - 尽管标准英语 FOCUSES 听起来不像 FOCI 那样夸张。