单项选择题
You'd better add it up. I'm not good at ______ .
单项选择题 The tide has ______ and left many beautiful shells on the beach.
单项选择题 When I came through the customs at the airport, I had to pay ______ on a camera I had bought.
单项选择题 The cottage ______ in the woods was built by George's great-grandparents.
