1．(2019·南通调研)Now all of our concentration is on ________ it is that the global environment will return to normal.
A．which B．what
C．where D．when
D 解析：句意：现在我们的注意力都集中在地球环境何时回归到正常状态。空及空后是介词on的宾语从句，宾语从句又用的是强调句型。强调句型特殊疑问句的结构为：特殊疑问词＋is/was＋it＋that＋不被强调的部分。由于题干中的强调句作宾语从句，应用陈述语序。从句中缺少时间状语，也就是缺少被强调的部分。故选D。
2．(2019·淮安调研)The three travelers finally reached the home of Bertha’s mother around dusk, ________ 65 miles in less than 12 hours.
A．covering B．having covered
C．to cover D．to have covered
B 解析：考查现在分词完成时作状语。因为cover与three travelers是主动关系，并且发生在谓语动词动作之前，故选B。
