Sediments in sedimentary rocks are often
a) held together with natural cements
b) formed when atoms of melted minerals rearrange themselves
c) formed when lava erupts from a volcano
d) formed by magma trapped below earth's surface

Sedimentary rocks set up  through the discharge and freezing  of sediment which is transported by water and crystallize between sediment grains this procedure is called cementation.
therefore,
Sediments in sedimentary rocks are often held together with natural cements.
hence the right answer is A) held together with natural cements

Sediments in sedimentary rocks are often held togheter with natural cements.

Air pollution: “combustion results in gases such as nitrogen oxides, nitrogen dioxide and particulates. the main causes of air pollution include transport, domestic combustion and industrial processes. pollutants from these sources can cause problems in the immediate vicinity and a distance away.”

Magma is outside the volcano  and lava is inside the volcano.