Read these passages: MACBETH. Stars, hide your fires
Let not light see my black and deep desires.
-William Shakespeare, Macbeth, Act I, scene iv
LADY MACBETH. Come, thick night,
And pall thee in the dunnest smoke of hell,
That my keen knife see not the wound it makes.
-William Shakespeare, Macbeth, Act I, scene v
These lines help to create a scary tone by:

the tone of the passage is sympathetic to the forbidden love of romeo and juliet. the nurse plays a significant role in the play. she is responsible for making their meeting again possible. additionally, there is a sense of warning in the choice of words of the nurse. she seems to be authoritative when she calls romeo "scurvy knave", and at the same time the fact that she addresses to him as "sir" reflects respect. the nurse is "vexed", this word describes her confused state of mind. on the one hand, she finds romeo a fine and eloquent man, but on the other, it is thought that man's nature forces men to try to trick women.  

a. "to practice" is the best phrase to complete the sentence.

explanation:

during the summer, she likes to practice her soccer skills so that she is ready to play in the fall.

(note that : all the other options "the practicing of", "practice for" and "to do a practice on" are inappropriate as they make the sentence grammatically incorrect.)