counterboring with step core drill

例句：

1. 1. The engineer counterbored the hole to make it larger.
   工程师将孔洞钻大以便通过。
2. 2. Thedrill penetrated the rock with ease.
   钻头轻松地穿透了岩石。
3. 3. The tunnelwas bored through the mountain for a newroad.
   为了一条新路，隧道穿过了这座山。