Answer:
1. I never brush my teeth- j. so now, I have tooth decay. 
2. School was cancelled- d. so we decided to go to the mall. 
3. The boy was quiet in class- i. that's why the teacher gave him a reward. 
4. It rained- h. that's why Chris got wet. 
5. John forgot to close the gate- b. so the dog went out to the street. 
6. It was very hot outside- a. that is why the children were thirsty. 
7. Lina skipped her breakfast- c. that's why she was hungry at lunch. 
8. The boat had a leak- g. so it sank. 
9. Father wanted a bigger car- f. that's why he sold the old car. 
10. The family had visitors- e. so Karla helped clean the house.
Step-by-step explanation:
In the given two columns, side A contains the list of events that focuses on the reason while column B contains the effects of the causes in A. To pair the two columns with their corresponding causes, reading and understanding the phrases/ clauses is important. 
The correct pair of columns A and B are as follows- 
1. I never brush my teeth- j. so now, I have tooth decay. 
2. School was canceled- d. so we decided to go to the mall. 
3. The boy was quiet in class- i. that's why the teacher gave him a reward. 
4. It rained- h. that's why Chris got wet. 
5. John forgot to close the gate- b. so the dog went out to the street. 
6. It was very hot outside- a. that is why the children were thirsty. 
7. Lina skipped her breakfast- c. that's why she was hungry at lunch. 
8. The boat had a leak- g. so it sank. 
9. Father wanted a bigger car- f. that's why he sold the old car. 
10. The family had visitors- e. so Karla helped clean the house.