The correct answer is D. accelerate
It means to speed up progress of something, to hasten something.
If you had put them there already then those are correct
Determined is defined as <span> having a strong feeling that you are going to do something and that you will not allow anyone get in your way.
Stubborn is defined as </span><span>having or showing dogged determination not to change one's attitude or position on something, especially in spite of good arguments or reasons to do so.
Connotation of determined and stubborn is being strong-willed and resolute. When you are determined, you have decided to do something. When you are stubborn, in doing what you have to do and presented with arguments, you still decided to continue what you are doing regardless of what others say.
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