In the given sentence, 'has always...' refers to something that has been present from the past times, and is relevant to the present as well.
Also, 'has' is a helping verb that forms the present perfect tense with the main verb (past participle). (Present perfect tense indicates that an action began in the past and has just completed, or in this case, a fact that was and is still true.).
The standard structure of a verb phrase in the present perfect tense is:
has + past participle
Hence, the correct option must be a past participle.
Option C: 'Been' is a past participle of 'to be'. Hence C is the correct option.
Options B and D: 'Is' and 'was' cannot be used as a main verb, when there is a helping verb already in the sentence. They are either used as helping verbs themselves, or used alone as a main verb, without an auxiliary.
Option B: 'Be' is the base verb and cannot be used in this form in a sentence.
Hence options A, B and D are incorrect.