这到底是个什么句子，请高人帮忙分析一下？

Fall is the season when people in the U.S and Canada celebrate Thanksgiving.
首先想问一下“relative clauses of time”怎么翻译？是关系从句吗？
但是这样翻译好别扭呀。好像上学的时候老师不是这么说的。
第二个 用When引导的是个什么句子？

relative clauses of time 关于时间的从句

When 引导的是时间状语从句, 表示在引导词的期间内进行的行为.

relative clauses of time 关于时间 (hope that helps) What are relative clauses? A relative clause begins with a relative pronoun (who, whom, whose, which, that) and tells something about a noun in a sentence. She did not want to donate money to an agency that would waste funds. He found his wedding ring, which had fallen to the bottom of the pool. Similar adjective clauses can be written with when or where. The guidelines are the same. Spring is the time when the robins return and the daffodils bloom. I shopped at Bargain World, where I found lots of cleaning supplies. When are commas needed with relative clauses? Commas are used only if the relative clause does not restrict or identify the noun it modifies. In the first sentence above, the relative clause is restrictive because it is needed to identify which type of agency the woman does not want to support. In the second example, the relative clause in nonrestrictive, meaning that "wedding ring" is not further identified by the clause "which had fallen..." In other words, that clause does not tell us what ring or what kind of ring; it only adds information about the man's wedding ring. Here are some examples of each type of relative clause. Restrictive (does not have commas) His campaign promise was to listen to the people who live in this district. (The clause restricts "the people" to those who live in one district.) The machine which sorts the mail is broken. (The clause tells us which machine.) Nonrestrictive (needs commas) My sister, whose arm is sprained, is supposed to give a recital Friday. (The clause is not meant to tell us which sister; maybe the writer has only one sister. The clause just adds information about the sister.) Parkville, which is expanding quickly, needs to build another elementary school. (The name "Parkville" identifies the town, so the clause can not restrict it further.) Common mistakes with relative clauses The most common mistakes which writers make are leaving out the relative pronoun and getting confused about whether a relative clause needs commas or not. Some sentences with mistakes: The thief left the money on the counter ran away quickly, but the other thief tripped and fell. The story says that Jonah who was a stubborn man spent some time in a whale's belly. People, who live in this city, have many choices for transportation. Here are the correct versions. The thief who left the money on the counter ran away quickly,... (If you see two verb phrases with no connecting word, such as "left the money ran away quickly," something is wrong with the sentence. In this case, to fix it use a relative clause, but don't forget the pronoun who.) The story says that Jonah, who was a stubborn man, spent some time in a whale's belly. (Jonah is already one specific person, so the clause can not be restrictive.) People who live in this city have many choices for transportation. (restrictive clause)