explain的名词形式是explaination还是explanation.

是explanation.
a statement or account that makes something clear
解释；说明
the birth rate is central to any explanation of population trends.
出生率是说明人口趋势的关键.
■a reason or justification given for an action or belief
原由；解释
Freud tried to make sex the explanation for everything.
弗洛伊德试图用性来解释一切.
[mass noun]my application was rejected without explanation.
我的申请被无缘无故地拒绝了.
祝楼主进步!