The complete subject in the sentence is "picnic".
The subject of a sentence is what is performing the action in that sentence. This can be a person, place or a thing.
An example where the subject of a sentence is a place is illustrated below:
Here the 'picnic' is used as a subject which is a place in the sentence.
Therefore, the complete subject in the sentence is "picnic".
Learn more about subject here:
https://brainly.com/question/18735
#SPJ1