Given that the conditions in binary star systems should make planetary formation nearly impossible, it's not surprising that the existence of planets in such systems has lacked _ explanation. Roman Rafikov and Kedron Silsbee shed light on the subject when they used modeling to determine a complex set of factors that could support planets' development. Which choice completes the text with the most logical and precise word or phrase?

Explanation

Choice B is the best answer because it most logically completes the text's description of efforts to explain the existence of planets in binary star systems. As used in this context, describing an explanation as "a straightforward" one would mean that the explanation is direct and uncomplicated. The text asserts that since it should be "nearly impossible" for planets to form in binary star systems, it's "not surprising" that there isn't a straightforward explanation for the existence of planets in such systems; the fact that one potential approach involves "complex" factors offers further contextual support for this idea.