When I try to understand ----------that prevents children fr

When I try to understand __________that prevents children from getting fat,it seems to me that there two reasons.
a.why it is
b.what it is
为什么不选A?要选B?
Please tell me _________you want your coffe,black or white?
a.how
b.which
为什么选A?不选B?
I think father would like to know ________I've been up to so far ,so I decide to send him a quick note.
a.why
b.what
为什么选b?不选a?
______ the olympic games will be held in beijing is not known yet.
a.whether
b.whenever
为什么选A?不选B?
I remeber ________this used to be a quiet village.
为什么要选when?
什么时后才用when和where做连接词?
怎样区分插入语?
eg.We agree to accept whoever they thought was writer.
they thought 为什么是插入语
不好意思.
______ the olympic games will be held in beijing is not known yet.
a.whether
b.whenever
我想问一下……
做题时应该先做什么？
先翻译句子还是判断句子是否缺什么成份？
this is the place ____i grow flowers on.
i grow flowers on是不是缺了宾语？
定语从句where which 怎样用？
说的好会加分的！