Multiple choice (A)Oil has and (B)still is (C)in great demand. (D)No error (A) (B) (C) (D) Reveal answer Fill a bubble to check yourself A Correct answer Explanation When two auxiliary verbs are used with a single principal verb, both must be correctly formed. 'Has' requires 'been' (past participle) to form the perfect tense, while 'is' works with 'in great demand.'