Hospital staff burst into cheers after doctors completed a 20-hour operation to have _______one-year-old twins at the head.

I found the island a wonderful place for our experiments _______ the hot weather

If we don’t do ______, soon giant pandas will die.

Would you please repeat the grammar rules again? —Of course, but I am sure that you _______ to me carefully, as I have told you twice already

________ Lily is only 13 years old, she knows 2000English words.