evenif不是不能放在句首嗎？

能放在句首也能放在句中

even if 引導的從句是往往是假設性的，相當于漢語的“即使”“縱然”“就算”“哪怕”。如：

They'll stand by you even if you don't succeed. 即使你不成功，他們也會支持你。

Even if I have to walk all the way I'll get there. 即使我得一路走著去，我也要走到那里。

Even if it rains tomorrow, we won't change our plan. 即使明天下雨，我們也決不改變計劃。

For my part, I plan to go to the party even if you decide not to go. 至于我，即使你決定不去參加晚會我也會去的。

even if與even though的區別：

even if一般引導的是把握不大或假設的事情,even though引出的是事實.

如：Even if we achieve great success in our work,we should not be proud.即使我們在工作中取得了巨大成績,也不應該自滿.

Even though he was late,he was not criticized by the teacher．雖然他晚了,可他并沒有受到老師的批評.

Even though he knows it,he'll not let out the secret.（他知道這個秘密）.

Even if he knows it,he'll not let out the secret.（不確定他是否知道這個秘密）.