Although It is part of the challenge to dig tunnel out of mud and cornerstones, a more fearful task is to accommodate large amount of fuel-eating cars and trucks that keep emitting poisonous gases.
Digging a tunnel out of dirt and rocks is a part of the challenges, but the more fearful task is to contain the large number of cars and trucks that are oil-consuming and are constantly emitting toxic exhaust.
is just part of the challenge, nevertheless, a more daunting task is to accommodate the large numbers of gas guzzling cars and trucks that are discharging toxic emissions non-stop.
Digging a tunnel through mud and rock is part of the challenge, but accommodating the large numbers of gas-guzzling cars and trucks that continue to emit toxic exhaust is even more frightening.
【中译英-from Chinese to English】
从泥土和基石中挖出隧道是挑战的一部分，但是更令人畏惧的任务则是去容纳大批量那些耗油（吃油）的、不停地排放有毒废气的汽车和卡车。
Bonus: 【英译中】（这是我在头条上看到的）
I miss you, but I miss you.
有人说，这个时态有错，其中一个应该是过去时。看到头条里有人译得非常好。等大家试试后再公布。
Although It is part of the challenge to dig tunnel out of mud and cornerstones, a more fearful task is to accommodate large amount of fuel-eating cars and trucks that keep emitting poisonous gases.
英译中：
I miss you, but I miss you.
我想念你，但是失去了你。
再译：
我念我所失，我失我所念！
从泥土和基石中挖出隧道是挑战的一部分，但是更令人畏惧的任务则是去容纳大批量那些耗油（吃油）的、不停地排放有毒废气的汽车和卡车。
Digging a tunnel out of dirt and rocks is a part of the challenges, but the more fearful task is to contain the large number of cars and trucks that are oil-consuming and are constantly emitting toxic exhaust.
英译中:
I miss you, but I miss you.
我想念你，但是我担忧你。
我念我所失，我失我所念！
is just part of the challenge, nevertheless, a more daunting task is to accommodate the large numbers of gas guzzling cars and trucks that are discharging toxic emissions non-stop.
I miss you, but I miss you.
曾为你五百次回眸，却终究擦肩而过。
Credit: 席慕容
I miss you， but I miss you.
心心念念忆相逢。别恨谁浓。
Credit： 《风入松》
晏几道 （宋）
中译英：
从泥土和基石中挖出隧道是挑战的一部分，但是更令人畏惧的任务则是去容纳大批量那些耗油（吃油）的、不停地排放有毒废气的汽车和卡车。
Digging a tunnel through mud and rock is part of the challenge, but accommodating the large numbers of gas-guzzling cars and trucks that continue to emit toxic exhaust is even more frightening.
英译中：
I miss you, but I miss you.
我想你，对你有着无尽的思念。
英译中意思有点出入了。第一个miss和第二个miss意思上好像不同。
这个“完美”原文好像没有？