____植物具有真正的根、茎、叶。

      Richard found a job in a big office after he finished college. He liked to use his 1 and was good at his job. So he was often paid more than (得到的报酬多于) his workmates and he worked 2. But something was wrong with the young man a month ago. He couldn't fall 3at night. So he was always 4 in the daytime and often made mistakes. He had to go to a hospital. The doctor5and told him to buy some sleeping pills. He took them6he went to bed. Soon after that he went to sleep. Richard7 in the morning. He had a look at the clock on the wall. It was a quarter to seven. He got up and went to work after8 . As soon as he went into the office, he said to the head of the office, "Good morning, Mr Clarke! I've9had a good sleep like last night's and I'm feeling much better now!" "Skunk (混蛋)!" the head10 loudly. "We've looked for you for two days! I wanted you to do something important, but it's too late now!"

设实数x,y满足约束条件$\{\begin{array}{c}3x-y-6\le 0\\ x-y+2\ge 0\\ x\ge 0,y\ge 0\end{array}$，若目标函数z=ax+by（a>0,b>0）的最大值为12，则ab的取值范围是（   ）

根据课文的意思判断对错。