题目选项分析

Most of Western music since the Renaissance has been based on a seven-note scale known as the diatonic scale, but when did the scale originate? A fragment of a bone flute excavated at a Neanderthal campsite has four holes, which are spaced in exactly the right way for playing the third through sixth notes of a diatonic scale. The entire flute must surely have had more holes, and the flute was made from a bone that was long enough for these additional holes to have allowed a complete diatonic scale to be played. Therefore, the Neanderthals who made the flute probably used a diatonic musical scale.

In the argument given, the two portions in boldface play which of the following roles?

【选项】The first is an opinion, for which no supporting evidence is presented in the argument given, that is used to support the main conclusion of the argument; the second is that main conclusion.