On the usage of the expression “What differentiate(s)”?
**Question one:** Which of the following sentences are grammatically correct? 1) What differentiate apples from oranges are their colors and sizes. 2) What differentiates apples from oranges is their colors and sizes. 3) What differentiates an apple from oranges is its colors and sizes. 4) What differentiates an apple from oranges are their colors and sizes. 5) What differentiate apples and oranges are their colors and sizes. **Question two:** Do you have any alternatives for the above sentences? I've searched the web to understand which expression to use, but I could not find a specific rule.