The answer is D, a writing system
I suggest you to go with first one a. there was heavy damage only within a mile of the bomb's impact. There're no closer description than that.
The French invasion of Vietnam was very gradual and it was going on step by step for quite some time. Initially, France was sending missionaries in Vietnam in order to spread the religion and culture of France in order to set basis for further actions. The missionaries indeed had very large influence, but came to a big resistance by the local courtesans who had feared for their status in the society if the French missionaries continued their work.
That led to some tensions and an attempt to banish the missionaries, but the French intervened with their military and stopped that. Since that initial military conflict, the French started to invade Vietnam. It was a step by step invasion, where the French would have invaded a city, than another city, maybe lose some afterwards, but than return and reclaim it, and that went on for some time until the French managed to totally outmaneuver the Vietnamese and gain control over their territory.
