若这次航行共消耗柴油15L，则柴油发动机的效率是多大？

将一个边长为10cm正方形，沿粗黑实线剪下4个边长为____ cm的小正方形，拼成一个大正方形作为直四棱柱的一个底面；余下部分按虚线折叠成一个无盖直四棱柱；最后把两部分拼在一起，组成一个完整的直四棱柱，它的表面积等于原正方形的面积．

秦岭的走向是（    ）

根据短文内容，选择方框内的单词, 并用其适当的形式填入空白处，使短文意思连贯通顺，语法正确。

Duties of a Student

    Education is the very thing that we want to receive. Our parents ____ us to school so as to enable (使能够) us to get knowledge and achieve great things in the future. The followings are the duties of a student which we should keep in ____.

    Firstly, we should be filial (孝顺的) to our parents and respectful to our ____.

    Secondly, we must study as ____ as we can.

    Thirdly, we must not tell lies.

    Last of all, we must not criticize (苛求) ____.

    To sum up, the above-mentioned rules are the very duties of a student.