开始认真的英文：
buckle down to

参考例句：

They've got the system down pat. He has the lesson pat.
他们开始认真考虑这种制度。他对这课学得很快

When you really get down to it, the noise and distractions aren’t really obstacles at all.
当你真正的开始认真考虑它的时候，嘈杂和干扰都不再是障碍。

If we all set to, we can finish cleaning the house in an hour.
如果我们开始认真干起来,我们一小时就能把房间打扫乾净。

buckle是什么意思：
n. 皮带扣，搭扣
v. 扣住；（使）变形，弯曲

He buckled the strap on.
他把皮带扣上。

The metal buckled in the great heat.
这金属在高温下变形了。

The parachutist was buckled into his harness.
跳伞者扣上了背带。

Belt buckle rash is a condition where skin reacts to the metal in a belt buckle.
皮带搭扣皮疹是指皮肤对皮带搭扣上的金属产生的过敏反应。

A freak wave had buckled the deck.
突然掀起的巨浪打弯了甲板。

down是什么意思：
prep. 在…下，沿着
v. 下降，打倒
n. 潦倒；羽绒；丘陵

Down with hegemonism!
打倒霸权主义！

The sun is down.
太阳下山了。

Close down autos and you close down steel and rubber.
关掉了汽车工业你也就关掉了钢铁工业和橡胶工业。

nail down; nail in;hold by
钉住;使人遵守诺言

break down resistance
粉碎反抗，制服反抗