just now,right now.

just now,right now.
我想问一下,
just now,
right now,
just at the moment,
at once,right away,
at the moment,
just then,
for a while,
这些短语的意思,哪些意思相近.谢谢.
还有这两题,选出与括号中意思相近的词
1.I am sorry I have not got any books about science (at the moment).
A.right now B.just now C.for a while
2.(Just at the moment)there was a knock on the door.
A.just now B.then C.just then