小题1:What is the colour of blood in a vein near the surface of the skin?
A．Blue.
B．Light yellow.
C．Red.
D．Dark reddish purple.小题2:Why do some old people look a little shrunken as they age?
A．Because their spine is in active use.
B．Because they are more easily affected by gravity.
C．Because they keep growing backwards.
D．Because their spine becomes more bent.小题3:Which of the following statements about our brain is true?
A．In the long run，our brain probably works harder than our heart.
B．When our brain senses the spinning，we will feel dizzy.
C．The brains of the other mammals are as complex as those of humans.
D．Our feelings and emotions come from the most developed area in our brain.小题4:What is the main purpose of the selection?
A．To give advice on how to stay healthy.
B．To provide information about our body.
C．To challenge new findings in medical research.
D．To report the latest discoveries in medical science.
，
B．
时满足题意，此时，a＞2a+3，解得a＜﹣3．
时，
，解得 a＞1．