15. Laurie did not do well in the first half of the course, but she made a substantial effort and improved her marks after the midterm. In this sentence, the word "substantial" means: a solid b. minimal c. free d. thick 16. My most humiliating day was when I left the zipper in my pants open. I was mortified when I found out that everyone could see the colour of my underwear! In this sentence, the word "mortified" means: a. excited embarrassed c. proud d. dead 17. The lake's water receded and moved back so much that the stumps of the logs were visible above the water. In this sentence, the word "receded" means: a. disappeared b. went down c. filled increased