Ⅰ.单句语法填空：根据句意，在空线处填上适当的连词。
1．(2019·天津市河北区高三年级总复习质量检测)It came as a great relief to the parents ________ their son finally came back safe and sound.
答案：that 这是一个同位语从句，从句中不缺成分，故填that。that引导的从句作relief的同位语。
2．(2019·广州市高三年级调研)Encouraging all boys to read nonfiction under the mistaken belief ________ it is their preference may actually be harmful.
答案：that 这里是一个同位语从句，说明belief的具体内容，从句中不缺成分，故填that。
3．(2019·山东潍坊高考模拟(七))It's estimated ________ producing one pound of beef requires seven pounds of feed.
答案：that 此处为主语从句，形式主语it替代主语从句，将that从句置于句末。“It＋系动词＋过去分词＋that从句”，故用that。
4．(2019·福建省高三毕业班质量检查测试)________ I didn't realize was that Orlando had to work that day too.
答案：What 设空处引导主语从句，在从句中作realize的宾语，意为“所……”，故用连接词What。
