Final answer:
Diffraction is more pronounced when waves pass through narrow openings that are comparable in size to the waves' wavelength, causing the waves to fan out. Thus, the correct answer is a) Narrow openings.
Step-by-step explanation:
The phenomenon where waves spread out after passing through an opening is known as diffraction. This fanning out of waves is especially pronounced when the waves pass through openings that are comparable in size to the wavelength of the waves. Hence, the fanning out is more pronounced through narrow openings, which in this context would be those whose widths are similar to the size of the waves' wavelength. Wide openings do not exhibit this effect as prominently because they are much larger than the wavelength of the waves. As a result, the correct answer to which type of opening would show more pronounced fanning out of waves upon passing through is a) Narrow openings.