A planetary nebula is a (ring-shaped) type of nebula formed by an expanding shell of gas around an aging star. *a planetary nebula is a type of nebula*. im not completely certain though. i might be wrong.
The answer is C “volcanic activity was more common in the past than it is today
Traditional Maasai society is organized according to age groups known as sets.
You might conclude that the ridge would get bigger and iceland would be halved
