The words "might" and "could" are modal verbs that both indicate a possibility or likelihood of an event happening. In the given sentence, "Olu might visit London next summer," the term "might" suggests a potential action in the future. Option A, "could," is the most appropriate choice because it is a modal verb similar in meaning to "might." Both convey the idea of a possible future action without guaranteeing it. The other options (will, should, can) do not precisely match the meaning of "might" in the given context.