The correct option is
B Look out
The exclamation marks in the given sentence indicate that it conveys either a command or an emotional outburst by the speaker. The second sentence explains a potential danger i.e "There is a scorpion under the bench!". Hence, the first sentence is most likely, a warning about the danger.
Option A: The phrasal verb, "Look out!" with an exclamation mark is said or shouted in order to tell someone they are in danger. Hence, option A is most appropriate.
Option B: The phrasal verb "Look over" means "to quickly examine".
Option C: The phrasal verb "Look after" means "to take care of".
Option D: The phrasal verb "Look for" means "to search for".
In the given sentences, the speaker is not asking the listener to examine/take care of/ search for anything. He is shouting out a warning. Hence, options B, C and D are incorrect.