1(i) - Simple present: I go to the school 
Simple past: I went to the school 

2(i) - Simple present: I write a letter to him 
Simple past: I wrote a letter to him 

3(i) -Simple present: She sings at Hard Rock Café 
Simple past: She sang ar Hard Rock Café 

4(r)- Simple present: He plays guitar 
Simple past: He played guitar 

5(i) -Simple present: Catarine buys gifts to her family 
Simple past: Catarine bought gifts to her family 

6(i) -Simple present: John understand the lesson 
Simple past: John understood the lesson 

7(i) -Simple present: My mom has a blue t-shirt 
Simple past: My mom had a blue t-shirt 

8(r) -Simple present: The teacher opens the window 
Simple past: The teacher opened the window 

9(i) -Simple present: I see a bird on the tree 
Simple past: I saw a bird on the tree 

10(r) - Simple present: My friend arrive today 
Simple past: My friend arrived yesterday 

I= irregular 
R= regular