Rút gọn biểu thức: $M$ = ($\frac{1}{\sqrt{a}-1}$ - $\frac{1}{\sqrt{a}}$) :$(\frac{\sqrt{a}+1}{\sqrt{a}-2}$ -$\frac{\sqrt{a}+2}{\sqrt{a}-1})$

Choose the best answer.

I think you should buy _____  pack of mineral water instead. And you can also buy _____  snacks such as potato crisps, 3 kilos of mandarins, 2 kilos of apples, 3 bunches of bananas, ______  cookies and soft candies.

Choose the best answer.

We should decorate our living room with _____ orange banner. We also need ________  ribbons, balloons, party hats and costume.

Choose the best answer.

I think that ______ cauliflower is not enough for 3 people. Let’s buy one more.