Agatha Christie wrote the following books from your list:
- Five Little Pigs
- N or M?
- Endless Night
The other books were not written by her.
Thus, the answer is b. 3. However, since that's not one of the options provided, if we assume the question's intent was possibly focused on books that might relate to her themes or style, we could suggest a re-evaluation.
However, based solely on the authorship:
- 1: Not by Christie (by Arthur Conan Doyle)
- 2: By Christie
- 3: Not by Christie (by E.M. Forster)
- 4: Not by Christie (by Arthur Conan Doyle)
- 5: Not by Christie (by Josephine Tey)
- 6: By Christie
- 7: By Christie
- 8: Not by Christie (by Arthur Conan Doyle)
So, to summarize, only 3 of the books listed were written by Agatha Christie. If you stick to the options you've given, the closest answer would be that only 3 books were written by Christie.