In terms of grammar, both are correct. However, they're used in different contexts. In the sentence "我外婆昨天去世了"， the emphasis is on the fact that this specific incident (grandma passed away) took place in the past. So let's look at it in the following context: - 你昨天去哪儿了，怎么没来上班？ - 我外婆昨天去世了，所以我没能来上班。 Or - 你怎么那么伤心，出什么事了？ - 我外婆昨天去世了。 In the sentence "我外婆是昨天去世的", the emphasis is on When did this specific incident take place (in the past). Let's look at the context: - 你外婆怎么突然去世了？！她 是 什么时候 去世 的？ - 我外婆 是 昨天 去世的。 So here we need to know that the construction "是 + when/where/how/with whom + v. + 的" is used to describe or ask about when/where/how/with whom DID an action take place in the past.

These two sentences have almost the same meaning, but still have difference in their emphase. The first sentence put emphasis on the time. "我外婆是昨天去世的。" , it can be translated into : "It's yesterday that my grandma passed away." The point is the time, because the verb in this sentence is "是". and the other sentence "我外婆昨天去世了。" It is explaining the fact that yesterday my grandma passed away. Hope it can solve your question :D

It would depend on the context. If someone asked you. 'When did your grandma die ?" then you would probably use the first one. If someone asked you why you are sad, then you could use the second. (btw I'm not a native speaker).

Thank you. 谢谢

兩個都可以