The restrictions imposed by China on rare earth metals has resulted in some companies (e.g., Toyota, Renault, Tesla) starting to look for alternatives. They plan to use parts that do not include rare earth metals. Is this a good solution?

Short term Yes,

Explanation: Japan recently stumbled upon a pile of rare metals and North Korea is currently sitting on the world’s largest wealth of rare minerals. As soon as North Korea denuclearized, sanctions will be lifted and foreign companies will rush in to grab a piece. Therefore in the long term, they can always source it from elsewhere.

Assuming China keeps the restriction on for the long term, then it would lose its competitiveness when newer players come in.

Yes

Explanation:

The most important way to ensure the existence of the human race is to ensure that our natural resources are not depleted such that we will pose environmental problem to our space, hence the restriction imposed by China on rare earth metals is a step in the right direction.

In addition to the above, these are resources that are non-renewable and in few decades to come, we might not be able to access these resources again, thus a need to ensure their availability for future use.

It can be concluded that this restriction will give room to look into another means of creating wealth as well as employment as we may have to invest into ideas that will generate an alternative to these resources.

This will also protect the environment as earlier mentioned.    

It's D

I believe it's capital because the economy's revenue cannot increase when there's a capital lol.

The economy's revenue cannot increase with natural resources(natural gas, etc), labor (jobs, etc), agriculture(plants to feed families, etc)