The meaning of "expired" as used in this sentence is: past the date of being safe to drink.
The sentence states that Benjamin made an awful face when he sniffed the milk in the jug and exclaimed, "This is definitely expired!" Based on this context, the meaning of "expired" in the sentence is "past the date of being safe to drink." Therefore, (1 point) "past the date of being safe to drink" accurately describes the meaning of "expired" as used in this sentence.