OBLIGATORY
Option D
Obligatory (لازمی) means required by a legal, moral, or other rule; compulsory.
Useful (مفید) means able to be used for a practical purpose or in several ways.
Stubborn (ضدی) means having or showing dogged determination not to change one's attitude or position on something, especially in spite of good arguments or reasons to do so.
Agreeable (خوشگوار) means pleasant.
Required (ضروری) means necessary according to rule or law, similar to obligatory.