The Australian boy has a good ________ of Chinese and can express himself freely in it.
| A．power | B．command |
| C．demand | D．usage |
—How can I use the equipment?
—Well, just refer to the ________.
| A．directions | B．explanations |
| C．expressions | D．introductions |
—Do you know why Jane was so angry?
—Her roommate gave in to ________ and opened the letter addressed to her.
| A．curiosity | B．consideration |
| C．concern | D．convenience |
In my brother's absence, I would like to thank all concerned on his ________.
| A．behalf | B．part | C．business | D．interest |
—What does PM 2.5 mean?
—It's a professional ________ indicating the condition of air pollution.
| A．term | B．item | C．number | D．mark |