1.1.What problem did the grandpa work out?

A A physics problem.

B A math problem.

C An English problem.

D A history problem.

解析：选A。A 细节理解题。根据第一段的 “In the video, an old grandpa helped a student with a physics problem.” 可知，爷爷解答的是物理题。故选A。

2.2.Where does Xiao Ren work?

A In a school.

B In a hospital.

C In a nursing home.

D In a restaurant.

解析：选C。C 细节理解题。根据第二段的 “The video was taken by Xiao Ren. He works in a nursing home in Henan.” 可知，小任在河南一家养老院工作。故选 C。

3.3.What was the grandpa’s job before?

A A doctor.

B A teacher.

C A driver.

D A cook.

解析：选B。B 细节理解题。根据第二段的 “Grandpa is 79 years old. He was a teacher before.” 可知，爷爷以前是一名老师。故选 B。

4.4.Why did Xiao Ren ask Grandpa for help?

A He was sick.

B He was tired.

C He was sad.

D He was busy.

解析：选D。D 细节理解题。根据第二段的 “Xiao Ren was busy, so he asked Grandpa to help the student.” 可知，小任因为太忙才请爷爷帮忙（给这个学生讲物理题）。故选D。