I’m not that sure, but there is a subordinating conjunction ‘if’, and ‘if the bus is late’ is a dependent clause, whereas ‘Britta will have to walk to work.’ is an independent clause, which makes it a complex sentence structure.
Let me start with why it isn't C. C is true but it's not more important than what A says. A talks about how Martin and Kennedy agree with their words which is what the question asks.
