B-Infinite phrase. This is the correct option.
As the band took the stage they asked everyone to look to the second stage where a giant, inflatable gorilla weaved its arms to everyone in attendance. The underlined structure is an infinite phrase because it is headed by an infinitive: " To look ". Then, it is a phrase because it can be substituted for a nominal phrase " something". The verb pattern is " to ask somebody something". What can this something be? "To look to the second stage."
These options are no t right:
A- participial phrase ( Example: The band suggested everyone looking to the second stage...)
C- main clause ( Example: The band asked the audience to look to the second stage after they finished their first song.)
D- subordinate clause ( Example: The band asked the audience to look to the second stage after they finished their first song.)