兩題英文文法不懂

1.Taipei's MRT Neihu Line,_____ the eastern district of Neihu to the rest of the city,will begin operation on 7/4.
為什麼答案是 linking 而不是 linked


2.Vitamin D is proven to be necessary for the prevention and ____of osteoarthritis.
a.it cures b.to cure c.cure d.cured
答案c為什麼
Update: 第一題

主詞是物可以改成如下嗎
Taipei's MRT Neihu Line, which is linked the eastern district of Neihu to the rest of the city,will begin operation on 7/4.
5 answers 5