. --- Sarah said she wrote you a letter.
--- I wonder ______ she is writing to me about.
| A．that | B．why | C．what | D．when |
It is uncertain____side effect the medicine will bring about，although about two thousand patients have taken it.
| A．that | B．what | C．how | D．whether |
The other day，my friend John drove his car down the street at _______I thought was a dangerous speed andsurprised everyone in the car.
| A．which，that | B．which，it | C．as，which | D．what，that |
The lack of eco-friendly habits among the public is thought to be a major ____ of global climate change.
| A．result | B．cause | C．warning | D．reflection |
Arriving home，the boy told his parents about all the________which occurred in his dormitory.
| A．occasions | B．incidents | C．matters | D．accidents |
There’s a _____ in our office that when it’s somebody’s birthday, they bring in a cake for us all to share.
| A．tradition | B．balance | C．concern | D．relationship |