宾语从句（Object Clause），指的是一个子句（从句）在主句中充当动词的宾语。
1. 宾语从句由连接词(从属连词、连接代词、连接副词)引导
1.1. 从属连词"that"、"if"、 "whether"
"that"：
He realized that he had left her phone at home. (他意识到他把手机忘在家里了。)
通常情况下，我们可以省略宾语从句中的 "that"：
She said (that) she is going to the store.（她说她要去商店。）
I believe (that) you can do it.（我相信你能做到。）
They hope (that) we will join them for dinner.（他们希望我们能一起吃晚饭。）
但是，但也有一些情况下我们不能省略 "that"。列举如下：
1）当主句的谓语动词与that引导的宾语从句之间有插入语时，that不能省略。
He mentioned, in his report, that the project is progressing well.（他在他的报告中提到，这个项目进展顺利。）
2）当that后面有插入语时，that不能省略。
She mentioned that, in her opinion, the project was a success.（她提到，依她的看法，这个项目是成功的。）
The professor explained that, according to recent research, the findings were groundbreaking.（教授解释说，根据最新研究，这些发现具有突破性。）
He declared that, without any doubt, the new policy should be implemented.（他宣布，毫无疑问，新政策应该被执行。）
3) 宾语从句作介词的宾语时，that不能省略。
She insisted on that he was innocent.（她坚持认为他是无辜的。）
4) 宾语从句后置时，用形式主语it前置到其原位，此时that不能省略。
They find it important that you understand the rules.（他们认为你理解规则很重要。）
I consider it necessary that you attend the meeting.（我认为你参加会议是必要的。）
5）当 "that" 引导的宾语从句在句子中充当双宾语结构中的直接宾语时，虽然在口语中可以省略that，但是书面语中（尤其是考试时）不要省略 "that"：
She told me that she likes her new job.（她告诉我她喜欢她的新工作）
6）谓语后有两个或两个以上宾语从句时，虽然在口语中可以省略所有that，但是书面语中（尤其是考试时）只有第一个that可以省略，后续的that均不能省略：
She said she will come and that she will bring a gift.（她说她会来，她还会带来一份礼物。）
He mentioned he likes swimming and that he enjoys hiking.（他提到他喜欢游泳，他也喜欢徒步旅行。）
"if"（是否）：
I wonder if he likes chocolate.（我想知道他是否喜欢巧克力。）
"whether"（是否）：
We are unsure whether it will rain tomorrow.（我们不确定明天是否会下雨。）
"if", "whether" 引导表示“是否”的一般疑问语气的宾语从句，二者通常可以互换。但是在以下情况时，两者不能相互替换使用：
1）当 "whether" 与 "or not" 搭配使用时，不能用 "if" 替换：
Whether he will attend the party or not depends on his schedule. (他是否参加派对取决于他的日程安排。)
I'm not sure whether or not they are coming to the meeting. (我不确定他们是否来参加会议。)
2）介词的宾语从句可以由 "whether" 引导，但不能由 "if" 引导。
She is concerned about whether the project will be completed on time. (她担心项目是否能按时完成。)
He is debating on whether he should accept the job offer. (他正在思考是否应该接受这份工作提议。)
3) 动词decide, doubt, wonder, question, consider, know, realize, understand, believe, ask（书面语）后使用 "whether" 引导宾语从句，而不能使用 "if"。
这些动词通常涉及决策、怀疑、疑惑等语境。
列举如下：
"decide" (决定):
They need to decide whether to invest in the project. (他们需要决定是否要投资这个项目。)
"doubt" (怀疑):
She doubts whether he will come to the party. (她怀疑他是否会来参加聚会。)
"wonder" (疑惑):
I wonder whether they have received my email. (我想知道他们是否收到了我的电子邮件。)
"question" (质疑):
They questioned whether the information was accurate. (他们质疑信息是否准确。)
"consider" (考虑):
We should consider whether this is the right choice. (我们应该考虑这是否是正确的选择。)
"know" (知道):
I don't know whether she will be able to make it to the meeting. (我不知道她是否能来参加会议。)
"realize" (意识到):
She realized whether she had left her keys at home. (她意识到她是否把钥匙落在了家里。)
"understand" (理解):
I want to understand whether they are coming to the party. (我想知道他们是否来参加聚会。)
"believe" (相信):
They believe whether the project will be successful. (他们相信这个项目是否会成功。)
"ask" (问), "ask"在书面语或尤其在考试时，应用whether:
He asked whether they had finished the report. (他询问他们是否已完成了报告。)
1.2. 连接代词who、 whom、 whose、 which、 what
"who"（指代人）：
I don't know who she invited to the party.（我不知道她邀请了谁参加派对。）
"whom"（指代人）：
He asked whom you saw at the park.（他问你在公园看到了谁。）
"which"（哪一个）：
Tell me which book you want to read.（告诉我你想读哪本书。）
"what"（指代事物）：
I don't understand what he said in the meeting.（我不明白他在会议上说了什么。）
1.3. 连接副词when, where, why, how, whenever, wherever,however
"when"：
Please let me know when you can come for the meeting. (请告诉我你什么时候能来开会。)
"where"：
She couldn't remember where she had left her keys. (她不记得她把钥匙放在哪里了。)
"why"：
He explained why he was late.（他解释了他为什么迟到。）
"how"：
He showed me how to solve the math problem.（他向我展示了如何解决数学问题。）
"whenever"：
She could figure out whenever her cat was hungry by its meowing.（她可以通过她的猫的喵喵叫声来判断猫何时饿了。）
"wherever"：
With just one boat, we can reach wherever we want to go on this river.（只要有一条船，我们能够到达这条河流上的任何地方。）
2. 宾语从句的时态：宾语从句的时态和语态通常取决于主句中的动词。如果主句是过去的时态，宾语从句也要是过去的时态:
He told me yesterday that they will visit Paris the day after tomorrow.（他昨天告诉我，他们后天会访问巴黎。）