单选题 . ①When selecting a nest, the female of the river blenny (a small fish) appears to be sensitive to both size and orientation. ②Blennies deposit their eggs preferably in nests under large stones and in nests facing southeast. ③Southeast-facing nests contain larger egg clutches, a fact that cannot be completely explained by differences in nest stone sizes. ④Moreover, in a recent study, current speeds upstream of the nest and at the nest entrance were similar for nests facing southeast and those facing in other directions. ⑤A southeast-facing entrance per se thus seems to be the specific nest feature preferred by females, rather than the effect of selective positioning on current at nest entrance. ⑥The reasons for this preference are unclear, however.22. The passage is concerned with which of the following ______

A、 determining the different ways in which current speeds can influence the nesting preferences of female river blennies
B、 establishing nest orientation as a determining factor in egg laying among female river blennies
C、 questioning the importance of nest size as an influence on egg laying among female river blennies
D、 comparing the features of female river blennies that face southeast with those of nests facing in other directions
E、 examining how female river blennies determine the relative importance of nest size versus nest orientation

【正确答案】 B

【答案解析】 B：本文最终的论证重点便是巢穴的朝向问题，因此选项B正确。
A：第④句排除了水流速度这一因素。
C：排除大小因素只是文章的细节。
D：属于细节。
E：文中没提鲶鱼是如何确定大小和朝向谁更重要的。