1.This book will show you __B__ can be used in other context

1.This book will show you __B__ can be used in other contexts.
A.how you have observed B.what you have observed
C.that you have observed D.how that you have observed
2.The reason is __C__ he is unable to operate the machine.
A.because B.why C.that D.whether
3.Mr.Zhang gave the textbook to all the pupils except __A__ who had already taken them.
A.the ones B.ones C.some D.the others
4.It’s the third time __C__late this month.
A.that you arrived B.when you arrived
C.that you’ve arrived D.when you’ve arrived
请认真详细回答为什么,不要敷衍了事,否则不但不追加分,