Match the following concepts.
| Column I | Column II |
|---|---|
| (a) ELISA | (i) Is based on the detection of antibodies against a pathogen |
| (b) PCR | (ii) Can detect very low amounts of DNA |
| (c) RNAi | (iii) Takes place in all eukaryotic organisms as a method of cellular defense |
| (d) Bt toxin | (iv) Exists as inactive protoxins but is converted into an active form due to alkaline pH |