Question

I ______ a tasty breakfast this morning. A) eats B) had ate C) ate D) had eaten E) have ate.

Answer 1

Thank you for asking the question!
The correct option is C .
I ate a tasty breakfast this morning. Other form of verb are grammatically incorrect. Eats is used in simple present continuous tense while have eaten is used in present perfect tense. And this sentence is not at all in present tense so this indicated that it's showing the action that have done in past. So simple past tense should be used.
Hope it helps.

Answer 2

Answer eaten

Explanation: Subject + had+ 3rd verb of eat.