Which sentence has an elliptical adverb clause with an understood word or words?       a.) it should be lowered when the sun sets. b.) the un building has more flags than rooms. c.) the american flag should be displayed on the right-hand side of any other flags if it is carried in a procession. d.) the flag should be flown every day unless it is raining.

B) The UN building has more flags than rooms.

Explanation: An elliptical clause ("than rooms.") has been used here to avoid repetition of the verb "have"; the full sentence would be "The UN building has more flags than [it has] rooms." Since this clause is a modifier of the verb "has," it has an adverbial function, therefore it is an elliptical adverb clause.

he or she may have a different tone of feelings.

if flooding were to go unchecked, steel support beams in buildings would rust.