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。
答對率 38%。
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。
填 them 之後會變成 …about 5,000 other islands, some of them are just rocks…，前後各是一個完整句子，中間只有逗號、沒有連接詞，這在英文裡不成立。中文可以一路逗號到底，英文不行。
把 them 換成 which，後半句就從獨立句子降級成形容詞子句，整句只剩一個主要子句。國中學過 I have two brothers, both of whom are doctors.——同一個結構，指人用 whom、指物用 which。
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.