Student or Learner
What is the explanation of the use of the first "the" in the sentence "The yolk of an ostrich egg is actually a single cell that is about the size of an orange"? Why can't we use "a" so it becomes a yolk of an ostrich egg...
Do we always use "the" before prepositional phrase starting with "of"?
Please be aware that I'm neither a native English speaker nor a teacher.