thumbtack的复数形式怎么拼写？

I press the thumbtack into the board with thumb.我用大拇指将图钉按在木板上.The thumbtack pricked his index finger.大头针扎了他一下手指.He pinned up the notice with a thumbtack.他用图钉将通知挂起来....

thumbtack的音标：thumbtack的英式发音音标为：['θʌmtæk]thumbtack的美式发音音标为：['θʌmˌtæk]...

n.图钉vt.用图钉钉住...