The salinity of the oceans is

In order to control environmental pollution,the Government of India has passed the .......... to protect and improve the quality of our environment.

How many sentences are correct?
$(1)$ $CNG$ burns most efficiently.
$(2)$ $CNG$ cannot be adulterated.
$(3)$ $CNG$ is cheaper than petrol and diesel.
$(4)$ In the $1990$s,Delhi ranked $4$th among the $41$ most polluted cities of the world.

The warm Peruvian current that appears every $5$ to $8$ years off the coast of South America in the eastern Pacific is known as:

Using Ahmed Khan's method in Bangalore,approximately $Q$ kilometers of road have been laid by the year $P$.

The quantity of $CO_2$ in the atmosphere is about (in $\%$)