单句语法填空
(1) (2016·全国Ⅰ)On my recent visit, I held a lively three-month-old twin that had been rejected by __________(it) mother.
(2) (2107·全国Ⅱ)However, the railway quickly proved to be a great success and within six months, more than 25,000 people were using __________ every day.
(3)(2018·全国Ⅰ)If you are time poor, you need run for only half the time to get the same benefits as other sports, so perhaps we should all give __________ a try.
(4) (2018·全国Ⅲ)When the gorillas and I frightened each other, I was just glad to find ________(they) alive.