'Exert' means to apply force on influence over something else, this can be in a negative or positive way. In this quotation, it means that language, if used correctly, has the ability to express a 'hidden power'. It's also worth mentioning that the simile is relevant as the moon has an influence on the level of tides on Earth.
The choice that avoids fragments to present the information clearly and correctly is, Mr. Lang's fundraiser was a success. Because of his teenage daughter's computer skills, his website received a ton of donations. People loved it. Her sleek design and funny videos attracted a large crowd. The correct answer is the last choice.
The answer is "A". The way you can tell is, it is basically just a summed up version of it. <span />
