TeachAI IBExam technique · Sciences
How to answer “I, II and III” multiple-choice questions
Combination questions give you three statements and four answers built from them. They look slow, but with a fixed routine you can usually remove two options before you have finished reading.
What the question is really testing
Each statement is a small true-or-false question. The four options then combine them, so you only score if you judge all three statements correctly. That is why these questions punish guessing: one wrong judgement leads you to the wrong option.
The good news is that you never need to judge every statement before you can act. One confident decision usually removes two options.
A four-step method
- Read the stem and underline what it is about (for example, the backbone of RNA, not the whole molecule).
- Judge each statement on its own and write T or F beside it. Do not let one statement influence another.
- Start from the statement you are surest of and cross out every option that disagrees with it.
- Only then decide between what is left, using the statement you were least sure of.
Write the T and F marks on the paper. Under time pressure, a judgement you made in your head is easy to lose.
Use one sure statement to remove options
Many combination questions use the layout below. If you are certain about a single statement, this is what remains:
| You are sure that… | Options that remain |
|---|---|
| I is false | Only C (II and III only) |
| II is false | Only B (I and III only) |
| III is false | Only A (I and II only) |
| I is true | A, B or D |
| All three are true | Only D (I, II and III) |
Check the layout every time: some questions pair the statements differently, and the method still works if you rebuild the table in your head.
Worked example
Which statements about the sugar-phosphate backbone of a strand of RNA are correct? I. Its bonds are formed by condensation reactions. II. Its sequence of sugars and phosphates carries the genetic code. III. It is a continuous chain of covalently bonded atoms. A. I and II only B. I and III only C. II and III only D. I, II and III
Check the explanation
B. Statement II is the one to be sure about: the backbone repeats sugar, phosphate, sugar, phosphate, so it cannot carry information. The genetic code is carried by the sequence of bases. Marking II as false leaves only B. Checking the others confirms it: each sugar-phosphate link forms in a condensation reaction (I is true), and every link is a covalent bond, so the backbone is one continuous covalent chain (III is true).
Traps that cost the mark
- A statement that is true in general but not about the thing in the stem.
- A statement that is half right: if any part of it is wrong, the whole statement is false.
- Choosing D because “everything sounds correct”. Test each statement as if you expected it to be false.
- Spending three minutes on one question. Make your best elimination, mark it and come back.
Check your own course
Assessment details and command-term definitions are set by your subject guide and can change between guide editions. Check the guide for your examination session and follow your teacher’s advice. The methods and examples above are written by TeachAI IB.
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