语序
从句用陈述句语序，即连接词 主语 谓语 其他。如：I don't know where he lives.
连接词
从属连词
that在从句中不充当任何成分，只起连接作用，可省略。
如：I believe (that) April is the hottest month in Thailand.
if/whether在从句中作成分，不可省略。
如：I don't know whether he will come home for the festival or not.
He asked me if/whether I was from China.
连接代词
what,which,who,whose,whom在从句中充当主语、宾语、表语和定语等，不可省略。
We never know what will happen inthe future！
We used a watch to see who was the fastest.
连接副词
when,where,why,how在从句中充当状语，不可省略。
如：I wonder how I should deal with myproblem.
I've finally realized why my grandparents loved drinking tea and collectingtea sets.
时态
需要性原则
当主句为一般现在时，从句的时态视客观需要而定。
如：I hear Joe left for Beijing yesterday.
They are talking about which team will win the basketball game.
呼应性原则
主句是过去时，从句相应用过去的某种时态。
如：Jane said she was shopping at this time yesterday.
He told me that he would take part in the high jump competition.
特殊性原则
表示客观事实、真理或自然现象，无论主句是什么时态，从句都用一般现在时。
Our teacher said that the earth goes around the sun.
He told me that practice makes perfect.
疑问词 不定式
“疑问词 不定式”构成不定式短语，这种结构可在句子中作主语、宾语、表语等。用于该结构的疑问词有：
what,which,when,where,how。
如：I really don't know what to write about.
I have learned how to solve the problem.
声明：整理自网络，仅供大家学习！
