根据题意得：4a-12＜0，
解得：a＜3．
故答案为：a＜3
用should 或shouldn't 填空。
1. All of us study hard and learn English well.
2. As a student, you eat in class.
3. You speak to your parents like this ,you must be polite (有礼貌)
4. You eat less and take more exercise if want ot be healthier and stronger.
5. My mother is very after work, I do some housework for her.
蛋白质的等电点指的是______。
A．蛋白质溶液的pH值等于7时溶液的pH值B．蛋白质溶液的pH值等于7.4时溶液的pH值C．蛋白质分子呈负离子状态时溶液的pH值D．蛋白质分子呈正离子状态时溶液的pH值E．蛋白质的正电荷与负电荷相等时溶液的pH值
