3) 片——份。 7）我去逛街，想买几双耳环。”双“ is OK. But in theory, "副” is the most suitable. However, in daily conversations, we girls often say "一对耳环“，”副“ is kind of formal.

1）我在这片沙漠看见了三匹骆驼。 good 2）前台那儿放着一堆箱子。 good 3）我们点四片牛肉吧。 Here "片“ it's not suitable. We do not use "片“ to order "牛肉” ，Maybe ”份“ 4）一群牛向我们前头出来了。”群“ is OK，but the sentence is not smooth. "在我们前头，一群牛出来了” 5）姐姐写完了一份论文，累死了。“份” is not suitable。Maybe “篇” 6）这位画家参加了第七届美术展览会。good 7）我去逛街，想买几双耳环。“双” is OK，maybe “副” is good Hope to helpful to you.

3）四片牛肉？ 饭店里牛肉是按“片”卖的吗？ 5）一篇论文。 其他的没什么问题。