Question

The train arrived late what
is the helping verb in the sentence​

Answer 1

Answer:

I don’t think there is any grammatical mistake. One of the dictionary definitions of 'just now' is 'a little time ago'.

I can imagine myself waiting to meet someone (Fred) arriving on a train, then telling someone else: "The train arrived just now, but Fred wasn’t on it."

An alternative would be "the train has just arrived".

Answer 2

The helping verb in this sentence is ‘is’