Q13:
Like the grassy fields and old pastures that the upland sandpiper needs for feeding and nesting when it returns in May after wintering in the Argentine Pampas, the sandpipers vanishing in the northeastern United States is a result of residential and industrial development and of changes in farming practices.
A.the sandpipers vanishing in the northeastern United States is a result of residential and industrial development and of changes in
B.the bird itself is vanishing in the northeastern United States as a result of residential and industrial development and of changes in
C.that the birds themselves are vanishing in the northeastern United States is due to residential and industrial development and changes to
D.in the northeastern United States, sandpipers’ vanishing is due to residential and industrial development and to changes in
E.in the northeastern United States, the sandpipers’ vanishing, a result of residential and industrial development and changing
Why the key is B but not D? Please help!Thanks!
Q20:
The first trenches that were cut into a 500-acre site at Tell Hamoukar, Syria, have yielded strong evidence for centrally administered complex societies in northern regions of the Middle East that were arising simultaneously with but independently of the more celebrated city-states of southern Mesopotamia, in what is now southern Iraq.
A.that were cut into a 500-acre site at Tell Hamoukar, Syria, have yielded strong evidence for centrally administered complex societies in northern regions of the Middle East that were arising simultaneously with but
B.that were cut into a 500-acre site at Tell Hamoukar, Syria, yields strong evidence that centrally administered complex societies in northern regions of the Middle East were arising simultaneously with but also
C.having been cut into a 500-acre site at Tell Hamoukar, Syria, have yielded strong evidence that centrally administered complex societies in northern regions of the Middle East were arising simultaneously but
D.cut into a 500-acre site at Tell Hamoukar, Syria, yields strong evidence of centrally administered complex societies in northern regions of the Middle East arising simultaneously but also
E.cut into a 500-acre site at Tell Hamoukar, Syria, have yielded strong evidence that centrally administered complex societies in northern regions of the Middle East arose simultaneously with but
My question: Why "that were" can be omitted here in the key E? | 
