These flowers are beautiful. They ..... expensive, weren't they. - No, they .....

1. The first blank requires a verb to agree with "flowers". Since "beautiful" is an adjective describing the flowers, and the next clause uses "expensive", the missing verb is likely "are".
2. The second blank is part of a question tag. Since the statement is "They are expensive", the tag should be "aren't they".
Answer: are, aren't