What is Plasmodesmata?

Plasmodesmata are :

Inter cellular spaces : Apoplast Plasmodesmata :________.

What is the role of plasmodesmata in a plant cell?

Match column I with column II and select the correct option from the codes given below. {:(,"Column I",,"Column II"),(A.,"Nucleolus",(i),"Lipid storage"),(B.,"Sphaerosomes",(ii),"Glycolate metabolism"),(C.,"Peroxisomes",(iii),"Transport of macromolecules"),(D.,"Plasmodesmata",(iv),"RNA synthesis"):}

What is sternum ? What is its importance ?