Much to the couple’s comfort, their income is now double ________ it was five years ago. 

Nowadays school bus safety has drawn much attention nationwide for children’s safety is _______ worries parents most.

—I drove to Zhuhai for the air show last week..—Is that ________ you had a few days off ? 

With time going by, we have come to realize that creativity is _______it takes to keep a nation highly competitive.

---I’ll ask the teacher about past tense. I’m very puzzled about it. --- That is just _____ most of our classmates have doubt.