The young couple wrote to Mr Grand to ________ his warm reception during their visit to his farm.[ ]

下列各句中，加点的成语使用恰当的一项是（ ）

Among the 15-year-old children, some ____ studying in university while others are still learning to read and write.

It’s not easy to learn English well. ________as much as possible is necessary. [ ]

下列有关应用文知识的表述，不正确的一项是（ ）