H4 Extension with Pending H1B extension with No receipt

Hi Anil, I have question regarding filing of my spouse H4 extension.
My H1B is expiring on Aug-26-2021, So my Employer filled my H1B Extension on July 28-2021 but he did not filed my spouse h4 extension along with that. He said he will file once he get the h1 receipt number. But still did not received receipt number yet.
what do we have answer for the below question in form I-539
3.a) Is this application based on a separate petition or application to provide your spouse, child, or parent an extension or change of status?

a. Yes, filed with this Form I-539.
b. No
c. Yes, filed previously and pending with U.S. Citizenship and Immigration Services (USCIS).

Can we select c as answer and keep empty for question number 3.b) receipt number if we did not receive receipt number.