With the gas _____, they had to quit the car and walked.

—Must I turn off the gas after cooking ?  --Of course . You can never be ___ careful with that.

    A．enough          B．too            C．so             D．very

Make sure the gas is turned off after a bath, which would ________ cause danger.

A．somehow         B．meanwhile         C．otherwise         D．furthermore

—Must I turn off the gas after cooking ? 

—Of course . You can never be _______ careful with

that.

A．enough          B．too            C．so             D．very

Today’s drivers may feel shocked by the high price of petrol when they drive to the gas station. However, the car industry has the technology to solve the problem. It’s the hybrid car（混合动力汽车）.
What is a hybrid car? Any car that uses two or more sources of power is a hybrid car. Most hybrid cars on the road right now are petrol-electric hybrids. The petrol-electric hybrid car is just what it sounds like — a cross between a petrol-powered car and an electric car.
A gas-powered car has a fuel tank（油箱）, which supplies petrol to the engine. An electric car, on the other hand, has a set of batteries that provides electricity for the car.
To be useful to you or me, a car should be able to run at least 300 miles (483 km) before refueling, be capable of(能够) being refueled quickly and easily and fast enough to keep up with the other traffic on the road.
A petrol car meets these requirements（要求）but produces a large amount of pollution. An electric car, however, produces almost no pollution, but can only go 50 to 100 miles (80 to 161 km) between recharging(充电). And the problem has been that the electric car is very slow and inconvenient to recharge.
A petrol-electric car combines the advantages of the two power sources into one system that uses both gas power and electric power. Some experts believe that the hybrid car is “the next generation of smart cars”. A hybrid car can go up to 50% further than a traditional car can on the same amount of gas! It saves driver’s money on gas and cuts air pollution!
【小题1】What do the underlined words “the problem” in Paragraph 1 refer to?