Join the sentences in two ways, with or without which/that.a) A lot of rubbish is floating in the sea. It is a real danger

a) A lot of rubbish floating in the sea is a real danger to health.

b) The problem of soil erosion which has occurred ever since the man began to destroy forests is discussed in this chapter.

c) Nuclear energy comes from the energy stored within the nuclei of atoms  which are the basic building blocks of all matter.

d) The best things in life such as water and air that we often take for granted are free. 

e) The manufacture of one PC requires 28kg of liquid chemicals which have to be neutralized by a further 11 kg of sodium hydroxide.