1.正确答案：A.open (adj.)
2.你说的是对的呀!keep 后是可直接加 v-ing (准确地说是动名词,不是现在分词) 作其宾语：
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.你说的是对的呀!keep 后是可直接加 adj.构成“系表结构”作谓语：
He kept silent during the whole meeting.
Keep calm when faced with danger.
4.但 "keep + 宾语 + adj." (在此 adj.作宾语补足语) 也是极其常见的呀：
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.你问的这题属何种情况相信你可以自己做出判断了.