There's a problem confusing me for quite a long time. Any help'll be grateful There's a sentence:"What our astronauts desire to do is walk in space." I 've seen such expression off and on as "What clause+is+verb(as predicate)+...". I sometimes talk in this way too. But wouldn't it be wrong in grammar? cause "is" can be a predicate. I'm confused.Thanks to all of you. I really appreciate it. I understand "what" clause is a subject clause. Maybe I didn't make myself clear. What confused me was the verb following "is" like "walk" in this case. If walk is a noun it is no problem. but if it's a verb how could I explain it in grammar rule? such as this: " What I have to do is do it right now." With your help, it really dawned on me that it's an infinitive construction with an ommitable "to" like 一 said. It took me some efforts to understand Luis' words. So in strictly written English, it could be "What I have to do is to do it right now."