Thank you for replying me.
Indeed I always make mistake while posting.
Please suggest me how did you use the spoiler tab. it wasn't visible to me.
Hi
rajatbanik ,
Please follow the rules of posting going forward. (I have edited this question now).
To answer your question.
Comma + FANBOYS Rule is used when we have two independent clauses joined together.
Here, in option A, the sentence is actually conveying a single meaning in the form of one clause by using the conjunction but.
A. Cristina started the test later than the rest of the students but was still able to complete it in the allotted time
A single clause that conveys the meaning that even though she started earlier, she was able to complete it on time.B. Cristina started the test later than the rest of the students, however she was still able to complete the test in the allotted time.
Here, there is a slight change in meaning. It is trying to convey two opposing ideas using However. But as per our original sentence, we mean to say that she did something good. Hence, a single meaning. Notice the use of word "still".c.
Even though Cristina started the test later than the rest of the students,
yet she was able to complete it in the allotted time.
D.
Having started the test later than the rest of the students, Cristina was able to complete it in the allotted time.
E. Cristina was able to complete the test in the allotted time, yet she started it later than the rest of the students.
Complete change in meaning.