他们争论的主要难题是，稀土金属如钕的生产通常用来制作磁铁。
The main bottleneck, they argue, could be the production of rare earth metals such as neodymium, which is often used in making magnets.
但是socrates所面临的主要难题是如何使经济恢复增长。
But Mr Socrates's main challenge is how to return the economy to growth.
保持太阳能电池板的洁净是安装太阳能装置的公司遇到的主要难题。
Keeping them clean is a major headache for the companies deploying the installations.
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