1.正確答案：A.open (adj.)
2.你說的是對的呀!keep 后是可直接加 v-ing (準(zhǔn)確地說是動名詞,不是現(xiàn)在分詞) 作其賓語：
It kept pouring down for five long hours and the city was flooded.
He kept telling the same old story,and nobody believed him any more.
Keep smiling!It was no big deal.
3.你說的是對的呀!keep 后是可直接加 adj.構(gòu)成“系表結(jié)構(gòu)”作謂語：
He kept silent during the whole meeting.
Keep calm when faced with danger.
4.但 "keep + 賓語 + adj." (在此 adj.作賓語補足語) 也是極其常見的呀：
Would you please keep your voice down?You're in the library.
You must turn on your radar and keep your eyes wide open in such a situation.
She put her hands in her pockets to keep them warm.
5.你問的這題屬何種情況相信你可以自己做出判斷了.