According to the Senior High School English Curriculum Guidelines, which of the following is NOT true about the textbooks for senior high schools?
(A) The textbooks are classified into two levels (level A-basic and level B-advanced) from the first year in senior high schools.
(B) When an activity involves more than one sub-skill, it is more challenging.
(C) The more guidance is provided for an activity, the easier and the more suitable it is for the basic level.
(D) The text difficulty results from content, vocabulary, structure, and processing load.