If you are operating out of a textbook or class syllabus, I would go back to these elements first. Any other options should be taken as secondary. For me, I think that there is a process of elimination. Option B is out because Lech Walesa was a freedom fighter in Poland and was not in the position of power to gun down anyone. The first option is vague in its own right because "the Berlin Wall" is not an event. It's a symbol where individuals were shot and threatened, but the manner of the question seems to imply an event where these elements happened. I am not convinced of letter C because while there was undoubtedly death involved in the building of the Canal, it does not seem to me that the building of the Canal was done with the element of "gunning down" children, and unarmed people. In my mind, I think option D is the best answer. The "children" element in the question can be broadened to include university aged children, and I think that the Chinese government's response to protesters at Tianmen Square was to gun down protesters. The protesters lacked any significant artillery and the response of tanks and troops entering the Square and opening fire would be more in line with the basic premise of the question:
The CRI broadcasted 'several thousand people, mostly innocent citizens' had been killed by 'heavily armed soldiers."