Being good to the old people is necessary for us.（同义句）
问题描述：
Being good to the old people is necessary for us.（同义句）
—is necessary for us — — good to the old people .
The word“o—”means “happen”.（写单词）
答
1It tobe(it的一个句型 it be adj+for sb.+to do sth)
2occur
[əˈkə:]
vi.
发生; 举行; 存在