5.
Your Answer is
Correct Answer is C
Explanation
The C/D options are both adverbials, modifying the two actions of dig and fill it, with means accompanying, and the lack of with will cause ambiguity, (fill it over a hundred eggs), so C is correct and D is wrong.
Item B: Before the underlined part is a complete sentence, if it is followed by a complete sentence, a conjunction is required.
Item A: The attributive clause guided by preposition + which modifies the front noun, time has nothing to do with the latter sentence, A is wrong.