Nobody knows for sure how dinosaurs died out 65,000,000 years ago. It _______ because of sudden changes of their living conditions.

You ________ touch the chemical, or you ________ get burnt.

— Is it good to look up every new word when I come across it in reading?—No，you _____，because you are likely to guess the meaning from the context,

 —Are you coming for dinner?　—I’m not quite sure. I ______ go to my uncle’s instead.

 Jack _______ swim when he was five years old.