the tudents give him a warm welcome的warm是什么意思

The tudents in my English class made lots of mistakes today.They _____trouble with the lessons.
A.must have B.must have had C.can have D.must be having
请问为什么选A啊,B,D分别错在哪呢?

英语翻译
tudents grapple with multiple,conflicting,and often confusing ideas while they learn scientific concepts.Research has shown that instruction is both effective and durable when teachers use students’ ideas as a starting point and guide the learners as they articulate their repertoire of ideas,add new ideas including visualizations,sort out these ideas in a variety of contexts,make connections among ideas at multiple levels of analysis,develop ever more nuanced criteria for evaluating ideas,and regularly reformulate increasingly interconnected views about the phenomena (1,2).We refer to this process as knowledge integration.
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第一个单词错了
Students grapple with multiple,conflicting,and often confusing ideas while they learn scientific concepts.Research has shown that instruction is both effective and durable when teachers use students’ ideas as a starting point and guide the learners as they articulate their repertoire of ideas,add new ideas including visualizations,sort out these ideas in a variety of contexts,make connections among ideas at multiple levels of analysis,develop ever more nuanced criteria for evaluating ideas,and regularly reformulate increasingly interconnected views about the phenomena (1,2).We refer to this process as knowledge integration.