请教几个英语从句的问题.what、that、which引导的从句
1.They are teachers and don't realize ( )to start and run a company.
A.what it takes B.what takes it
C.what they take D.what takes them
为什么?take在这里是什么意思?what在从句中当什么成分?
2.I have made it clear( )I will never go back on my word.
A.when B.that C.where D.however
为什么不选A?
3.( )Bob is good at football is known to us all.
A.What B.How C.That D.Which
为什么不选C?从句“Bob is good at football”并不缺少什么成分啊.