Question

ice forms in rivers in very cold places. sometimes, ice breaks in interesting ways. in 2019, an ice disk formed in a river in maine. a piece of ice broke off. the river flowed past the chunk. the ice turned and turned. as it did, the edges were smoothed. the ice looked like a perfect circle. it spun in the river. it was there for days before it melted. scientists say this does not happen often. the ice disk was on the news. people around the world saw it. they wondered how it came to be.
the formation was
○ warm
○ rare
○ helpful
○ dirty

Explanation:

El texto indica que los científicos dicen que este fenómeno no sucede con frecuencia, lo que coincide con la definición de "raro" (rare). Las otras opciones no tienen relación con la descripción del fenómeno.

Answer:

○ rare