David left, do you know?—No, which team is he _____now? [ ]
You may get lost easily in big cities like Beijing you have a map or a guide.
_______the f’rst photo, I’m watching TV______home.[ ]
The World Health Organization has given some advice onto protect us from being infected(感染) with H7N9.
The following chapters provide step-by-step instructions for practical _______ of genetic (基因)engineering to agriculture.