But the force of geographic conditions peculiar to America, the interplay of the varied national groups upon one another, and the sheer difficulty of maintaining old-world ways in a raw, new continent caused significant changes.
在这个句子中，一共有几个主语？
A、 1
B、 2
C、 3
D、 4
英语语法与句子写作

章节列表

Unit 1 Sentence Components I （句子成分 I）9Unit 2 Sentence Components II （句子成分II）9Unit 3 Subordinate Clause I （从句I）17Unit 4 Subordinate Clause II（从句II）15Unit 5 Basic Types of English Sentences（句子基本类型）10Unit 6 LBT Analysis（LBT长难句分析）17Final Exam25