Answer: C. I have no joy of this contract to-night: It is too rash, too unadvised, too sudden; Too like the lightning, which doth cease to be.
Step-by-step explanation: From the given lines spoken by Juliet in "Romeo and Juliet" by William Shakespeare, the one that support Tim's thesis that Juliet is capable of making mature, rational decisions, is the corresponding to option C, because in this lines she is recognizing that the promises of love she and Romeo have made to each other, are too sudden, which demonstrate that she can be mature and rational.