重10⁴N的汽车在公路上做匀速直线运动，它受到的阻力是车重的0.03倍，则汽车发动机的牵引力是多少N？

小明在学习物体浮沉条件时，由于调制食盐水密度的操作不够精准，导致实验中鸡蛋很难悬浮在食盐水中。于是他对实验进行了改进：分别用量筒和烧杯等器材配制了三杯不同质量分数的酒精溶液，其中图甲B烧杯中的酒精与水的体积比为9:6。用注射器吸取密度为0.9克/厘米³的食用油，分别在三杯酒精溶液中部注射一团油滴，一段时间后，如图甲所示。再过一段时间后，小明观察到油滴所处的状态如图乙所示。为此，他作了如下探究：

【提出问题】                 

【建立假设】假设一：可能是油滴的密度变小了。

假设二：可能是酒精溶液的密度变大了。

【实验方案】针对“假设一”的实验：用注射器吸取图乙任一烧杯中的油滴，将油滴注入到某一溶液中，观察其浮沉状况。

针对“假设二”的实验：先测定酒精溶液密度为ρ₁，敞口放置一段时间后再次测定它的密度为ρ₂，比较ρ₁和ρ₂的大小。

【得出结论】油滴密度不变，酒精溶液密度变大。

请回答：

阐明生命现象的规律，必须建立在阐明生物大分子结构的基础上，下列关于组成细胞的分子的说法，正确的是（  ）

下列仪器：①容量瓶②蒸镏烧瓶③漏斗④燃烧匙⑤天平⑥分液漏斗⑦胶头滴管，常用于物质分离的是

根据短文理解，选择正确答案。

    Teachers' Day is, interestingly, not celebrated on the same day all over the world. In some countries it is marked by a holiday, in others it is a working day.

    International Teachers' Day is celebrated on October 5. Being held ever since 1994, it is in honor of teachers' organizations worldwide. Its aim is to encourage supports for teachers and to meet the needs of students.

    China    In 1939, Teachers' Day was set for August 27, Confucius' birthday. In1951, the celebration was stopped. However, it was founded again in 1985, and the day was changed to September 10.

    India     Teachers' Day is celebrated on September 5 in honour of Dr. Sarvepalli Radhakrishnan, the second president of India, whose birthday falls on that day.

    Russia    In Russia, Teachers' Day was celebrated on the first Sunday of October between 1965 and 1994. Since 1994, the day is observed on the October 5, just the same day as World Teachers Day.

    The US    In the US, Teachers' Day is non-official holiday. It is celebrated on the Tuesday of the first full week of May. A number of activities are organized in schools to honor teachers. The celebrations can continue for the whole week of May.

    Thailand     In Thailand, National Teachers' Day is celebrated every year on January 16. The first Teachers' Day was held in 1957. The day is a holiday in schools.