Quins són els principals problemes que comporta la manca de transports públics a les grans ciutats del món?

The study of where things are 

Your answer is d. silli hope this ! : ) i left an explanation down below if you need it: a sill forms when hot magma squeezes between layers of rock to form a hardened sheet of rock. a sill is basically a tabular sheet intrusion between old layers of sedimentary rock, volcanic beds, or in the direction of foliation inherent in metamorphic rock. the word sill means a concordant intrusive sheet.

Answer a mineral that contains a combination of silicon, si, and oxygen, o, is a silicate mineral. hope it ^.^

The answer would be a.