The ancient Greek playwright Euripides followed the established conventions of verse composition less rigorously at the end of his career than at the beginning. Since the lines from a recently discovered Euripidean play adhere to those conventions as rigorously as do lines from Euripides' early plays, the recently discovered play must have been composed early in Euripides’ career.
Which of the following is an assumption made in the argument?
A：All of Euripides' plays were written in verse.
B：Euripides did not write any plays late in his career in which he imitated the style of his early plays.
C：Euripides grew increasingly unaware of the established conventions of verse composition as his career progressed.
D：Late in his career, Euripides was the only playwright of his day who consciously broke with the established conventions of verse composition.
E：Ancient playwrights tended to be less willing to violate certain conventions early in their careers than they were later in their careers