An increasing number of schools are experimenting with looping classes; that allows teachers to advance to the next grade level along with their pupils, to give students the opportunity to form long-term relationships with their instructors.
A) classes; that allows teachers to advance to the next grade level along with their pupils, to give
looping classes is plural and the phrase modifying it cannot be singular , which mean "that allows " is wrong
B) classes that allow teachers to advance to the next grade level along with their pupils and give
This statement is perfect , subject-verb agreement and parallelism is perefectly put here . HENCE RIGHT ANSWER
C) classes and allow teachers to advance to the next grade level along with their pupils and give
allow teachers phrase is supposed to modify the action of looping classes , which means it is dependent on the first phrase of looping classes, And will make it equal which is wrong here.
D) classes, which allows teachers to advance to the next grade level along with their pupils, giving
Missing parallelism , as all sentences seem to be in simple present which gets spoiled by "giving" in the end and Allows is singular and not acceptable
E) classes, which allow teachers to advance to the next grade level along with their pupils, giving
same as above , missing Paralellism .