With our country entering an aging society, ______ the retirement age is probably unavoidable.
Mary is the only one of the students in our class who ____ to the Great Wall so far.
Two years ago, the 9-year-old girl set up ___ organization named Angel to help ____ homeless.
For miles around me there was nothing but a desert, without a single plant or tree ______.
More and more people choose to shop in a supermarket as it offers a great ____ of goods.
So difficult ______ it to live in an English-speaking country that I determined to learn English.