During and immediately after the California gold rush, the

One thing about the verb+ing modifiers is that, they rather describe not a single factor but the gist of several factors. Let’s take this example; what factors are determining the shape of the ships? The factors are: 1. there was a gold rush in San F. Some goods were scarce; if some could give the consumers those goods, they would pay any price and the trader can make huge profits. For this the trader has to take a light ship with optimal cargo that can dart like a hare to the destination rather than crawl like a tortoise carrying a huge load. All these factors collectively determined the shape of the ships. How to express all these in one stroke? Using the ing participle is a good way of doing that. But the problem in using the present participle is that it is a timeless expression. When we say determining, we can mean determining in the past, now and even in the future. But the clippers ships are a thing of the past. We have no clippers ships presently. The ships died their natural death after the advent of steamer ships. So an expression that point out the past nature of the phenomena, will espouse the meaning better, given the context. That is the reason, I prefer B over A.
C and D are dropped because of the ‘which’ touch rule problem, while the demonstrative pronoun ‘this’ has no appropriate antecedent in E

Incidentally, I see no run - on either in A or in B, What follow the comma are modifiers in both cases, whether determining or a situation. Determining is an adverbial modifier and a situation is an appositive modifier. There are no two ICs in the sentences to render them run-on each other)