During the tang dynasty what was used to expand throughout the south

B: train

Explanation:

By context clues:

A: they used a, so we cant use airplane because it would have to be an airplane.

C: it wouldn't make sense if you said a junk was used

so the only reasonable answer is a train was used

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.

answer; rate;