To solve this problem, we need to identify the correct pair representing the causative agent of typhoid fever and the confirmatory test for typhoid. Let's analyze each option:$\newline \bullet$Option 1: Plasmodium vivax / UTI test$\newline$ - Plasmodium vivax is a protozoan parasite and a human pathogen that causes malaria, not typhoid fever.$\newline$ - UTI test is used to diagnose urinary tract infections, not typhoid fever.$\newline$ - Therefore, this option is incorrect.$\newline \bullet$Option 2: Streptococcus pneumoniae / Widal test$\newline$ - Streptococcus pneumoniae is a bacterium that causes pneumonia, not typhoid fever.$\newline$ - Widal test is used for the diagnosis of typhoid fever, but the causative agent is incorrect.$\newline$ - Therefore, this option is incorrect.$\newline \bullet$Option 3: Salmonella typhi / Anthrone test$\newline$ - Salmonella typhi is the bacterium that causes typhoid fever, which is correct.$\newline$ - Anthrone test is a chemical test for carbohydrates, not related to typhoid fever.$\newline$ - Therefore, this option is incorrect.$\newline \bullet$Option 4: Salmonella typhi / Widal test$\newline$ - Salmonella typhi is the correct causative agent of typhoid fever.$\newline$ - Widal test is the confirmatory test used for diagnosing typhoid fever.$\newline$ - Therefore, this option is correct.$\newline$Thus, the correct pair is Option 4: Salmonella typhi / Widal test.