Microtubules have an inner diameter of and an outer diameter of

Microtubules have an inner diameter of 25 nm and an outer diameter of 30 nm.

Explanation:

Microtubules is a microscopic tubular structure that is present in the cytoplasm of cells; they are polymer structures that form part of the cytoskeleton that gives shape to cytoplasm of eukaryotic cells and some prokaryotic cells. A microtubules can be as long as 50 nm in diameter. The average inner diameter of microtubules is 25 nm while that of the outer diameter is 30 nm.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.