Theory must be combined with practice.理论必须联系实际.请教这里为什么用过去分词combined?

Theory must be combined with practice.理论必须联系实际.请教这里为什么用过去分词combined? The theory must be put into practice before it is fully accepted. We must apply what we have learned to our daily work because in no case _A__from practice.A should theory be separated B theory should be separated C should theory separate D theory should separate请详细解释下为什么选A.顺便分析下这个 SAT MATH QUESTION 1） The sum of eleven different integers is zero.What is the least number of these integers that must be positive?2) In a certain game,each token has one of three possible values:1 point,5points or 10points.How many different combi theory must be combined with practice.为什么要用with.我查了一下combine是及物动词.可以直接带宾语呀 A new theory （ ） before it can be put into practice.(本题分数：2 分.)A new theory （ ） before it can be put into practice.(本题分数：2 分.) A、 must be tested B、 be tested C、 can be tested D、 to be tested must be what must be must be! His theory proves to be scientific. Their theory is going to be tested 英语翻译Relevance theory is not an approach that must be confirmed to,but rather an account that should better be applied to some phenomena in translation.The reason why this thesis would like to focus on this issue is because relevance theory is must be happy must be young must be beautiful 英语翻译The end of constitutionalism becomes maintenance of an inheritance from the Founders,who must be approached with a kind of reverence.Maintenance,accordingly,requires a new form of auto-theory.Originalism,in turn,is undermined by the belie be tied to sth.He is tied to this theory. Their theory is going to be tested out什么意思? His theory proved to be right.为什么不是His theory was proved to be right.?应该用被动啊? must be 同义词 must be后面是动原吗