It was a difficult time for the relatives of Missing MH370 passengers when they heard the bad news , but they didn't ________ hope.
A：give out
B：give off
C：give in
D：give up
通过实验比较，玉米幼苗在土壤浸出液中比在蒸馏水中生长得好，说明玉米幼苗的生长需要（ ）
