1）
it is that 句型若強調的主詞有二個
那 that 後面的動詞要用單數動詞還是複數？
看過二種
It is cars and factories that release a great deal of gas.
It's the clash of characters and plot that makes an interesting narrative.
2）
Only if vs Only when
我看到的only if例句會加逗號，only when 卻沒有，請問為什麼？
Only if the government will take some appropriate measures, will this intractable problem be tackled.
Only when you are in adversity will you learn who are your true partners.
Thanks!