It is surrounded by about 5,000 other islands, some of 17 are just rocks sticking out of the ground.
答案：(D) which
some of which 引導形容詞子句，which 代替前面的 5,000 other islands；若填 them 會造成兩個句子只用逗號相連而缺少連接詞，that 不能用在介系詞之後，those 則無法引導子句。
語意上 some of them 完全說得通，所以很多人毫不猶豫就選 them。問題不在語意，在結構。
這一格與語意無關，四個選項填進去意思都通，要看的是結構。填 them 之後會變成 …about 5,000 other islands, some of them are just rocks…，逗號前後各是一個完整句子，中間卻沒有連接詞，不符合英文文法。句子與句子之間一定要有連接詞，而關係代名詞身兼連接詞與代名詞兩種功能。選 which，兩個子句就有連接詞連接，後半句也跟著成為形容詞子句。英文語法習慣精簡，連接詞寫一次就夠：I have two brothers, 「both of whom」 are doctors. 這裡的 both of whom 等於 and both of them，不可寫成 and both of whom。先行詞是人用 who、是物用 which，本題的先行詞是 islands，所以用 which。前面例句的 whom 與本題的 which 都是受格。
some／most／all／none of which（其中一些／多數／全部／沒有一個，指物）、both of whom（兩人都，指人）。
Kizhi is an island on Lake Onega in Karelia, Russia, with a beautiful collection of wooden churches and houses. It is one of the most popular tourist 16 in Russia and a United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Site. The island is about 7 km long and 0.5 km wide. It is surrounded by about 5,000 other islands, some of 17 are just rocks sticking out of the ground.
The entire island of Kizhi is, 18 , an outdoor museum of wooden architecture created in 1966. It contains many historically significant and beautiful wooden structures, 19 windmills, boathouses, chapels, fish houses, and homes.
The jewel of the architecture is the 22-domed Transfiguration Church, built in the early 1700s. It is about 37 m tall, 20 it one of the tallest log structures in the world. The church was built with pine trees brought from the mainland, which was quite common for the 18th century.