There _____ a folk music concert in Xinjiang Opera Theater next month.
一般将来时。
根据next month可知本题谓语动词需要使用一般将来时态；There be句型的一般将来时态表示为：There will be…或者There is / are going to be…，故选D。
We _____ a party for Kate. It's supposed to be a surprise.
根据本题的语境可知，我们会为凯特举办一场聚会，那应该会是一个惊喜，由此可知用一般将来时“will+动词原形”，故选C。
—Why don't you buy the sweater?
—It's too _____,and I don't have enough money to buy it.
形容词义辨析。
nice意为“好的，漂亮的”；expensive意为“昂贵的”；popular“流行的；受欢迎的”；cheap意为“便宜的”。从“我没有足够的钱来买它”可以推断毛衣太昂贵，选择expensive，故答案为B。