67%
Help the cautious diner make a safe choice! Select ALL the options that correctly complete the sentence.
"I'm really not sure what's in this mysterious green soup. It _____ vegetarian, so you probably shouldn't eat it if you strictly avoid meat."
The correct answers are might not be and may not be.
Because the speaker says "I'm really not sure," they are expressing a negative possibility (there is a 50% chance it is NOT vegetarian). We use might not or may not for this.
Can't be and couldn't be would mean the speaker is 99% certain the soup is impossible to be vegetarian (i.e., they know for a fact it has meat in it), which contradicts "I'm really not sure."