How is your recent trip to Sichuan—I’ve never had ______ one before.

The palace is heavily guarded, because inside its walls ________.[ ]

nD helps our bodies make a special chemical，and this special chemical, ______affects our brains，making us feel happy

If nature doesn’t provide man with the necessary material, it is the laboratory _____ he will turn to for help.

Mr Brown asked me to remind you of the meeting this afternoon. Don’t forget it !–OK, I __________.