When the string player causes small pitch fluctuations by rocking the left hand while pressing the string down, it is called: ?

I think you are talking about vibrato. Vibrato- creating vibration in pitch or volume of a note. String players use their left hand to make these vibrations. Example: cellists usually use arm vibrato which is where the rock not only hand but also their arm to make the vibrations (violins usually only rock their hand).

I hope this helps!

C) The music bridges the cut to Robbie's hand-off of the letter to Briony.

Explanation:

According to a different source, these are the options that come with this question:

A) The music binds together the crosscut shots of Cecilia and Robbie.

B) The music conveys the feelings Robbie and Cecelia have for each other.

C) The music bridges the cut to Robbie's hand-off of the letter to Briony.

D) The music abruptly stops when Robbie rips a page out of the typewriter.

This is not one of the ways in which the aria functions as non-diegetic music. Diegetic music is music that comes from a source that is visible on screen, or that is included by the action of the film. Examples of this include the voices of characters or the music that comes from objects that are part of the story. On the other hand, non-diegetic sound refers to sound that is not included in the action of the story, such as mood music.