Question at position 17 Which of the following lines of code will run, but then give a runtime error?a = [1, 2, 4]print(a[2])a = [1, 2, 4]print(a[4])a = [1, 2, 4]print(a[1])a = [1, 2, 4]print(a[0]) Clear my selection单项选择题
A
a = [1, 2, 4] print(a[2])
B
a = [1, 2, 4] print(a[4])
C
a = [1, 2, 4] print(a[1])
D
a = [1, 2, 4] print(a[0])

Question

Question at position 17 Which of the following lines of code will run, but then give a runtime error?a = [1, 2, 4]print(a[2])a = [1, 2, 4]print(a[4])a = [1, 2, 4]print(a[1])a = [1, 2, 4]print(a[0]) Clear my selection单项选择题

A

a = [1, 2, 4] print(a[2])

B

a = [1, 2, 4] print(a[4])

C

a = [1, 2, 4] print(a[1])

D

a = [1, 2, 4] print(a[0])

BlackTom AI · Accepted Answer

Python uses zero-based indexing, so a list with three elements has valid indices 0, 1, and 2. Accessing an index outside that range does not produce a syntax error (the file still runs), but raises a runtime IndexError when the out-of-range access is executed.

Relevant knowledge points and concepts
- Zero-based indexing: for a = [1, 2, 4], indices are 0 -> 1, 1 -> 2, 2 -> 4.
- len(a) = 3, so valid indices are 0 through len(a)-1 = 2.
- Out-of-range access raises IndexError: list index out of range (a runtime error).
- Syntax errors prevent the program from starting; an IndexError occurs while running.

Step-by-step reasoning and intermediate steps
1. Determine list length: a = [1, 2, 4] => len(a) = 3.
2. Map indices to values:
   - a[0] = 1
   - a[1] = 2
   - a[2] = 4
3. Evaluate each option:
   - print(a[2]) tries index 2; since 2 <= 2, this is valid. Output: 4. No error.
   - print(a[4]) tries index 4; 4 > 2, out of valid range. At runtime Python raises IndexError: list index out of range.
   - print(a[1]) tries index 1; valid. Output: 2. No error.
   - print(a[0]) tries index 0; valid. Output: 1. No error.

Why the correct answer is correct
The only line that will run but then produce a runtime error is the one accessing a[4]. The code itself is syntactically correct so the interpreter runs it, but when it attempts to fetch index 4 from a three-element list, Python raises an IndexError.

Why the other options are incorrect
Each of the other print(...) calls accesses a valid index (0, 1, or 2) and therefore prints the corresponding value without an error.

Conclusion
The correct choice is:
a = [1, 2, 4]
print(a[4])
This matches the provided answer.

Question at position 17 Which of the following lines of code will run, but then give a runtime error?a = [1, 2, 4]print(a[2])a = [1, 2, 4]print(a[4])a = [1, 2, 4]print(a[1])a = [1, 2, 4]print(a[0]) Clear my selection单项选择题

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