Don't use water to put out the fire if oil catches fire. As is known, oil ________ float on water.

—David is often absent from class.—Tell him he ________ answer for it if he goes on behaving like that.

--- This must be a footprint of a tiger. --- It ____ be. A tiger’s should be much larger and deeper than this. 

------It took me about 40 minutes to ride here.------Have a drink ,please. You ________ be thirsty.

— I’m a little tired. Let’s go to the zoo by taxi.  —We ________take a taxi. It’s not far from here.