Constructing a couter from D-Flip-Flops

I have a assignment about constructing a two bit downwards counter with the help of D-Flip-Flops and NOR-gates.

We use Digital Fundamenmtals 10th edition, and it covers counters based on JK-Flip-Flops. So I don't understand how to do it with only D-flip flops.

What I have done:

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Counts from: 00 --> 11 --> 10 --> 01 --> 00....

Current state | Next state | Flip-Flop inputs

Q1 Q0----------Q1 Q0---------D1 D0
--0 0------------1 1------------ ? ?
--0 1------------0 0------------ ? ?
--1 0------------0 1------------ ? ?
--1 1------------1 0------------ ? ?
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How can I see what the states of the D inputs should be?

With JK inputs we use a table like this:
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|Output transitions --------- Flip-Flop Inputs |
| QN -- QN+1 ----------------- J ------ K --|
---------------------------------------------
--0 ---> 0 -------------------- 0 ------ X
--0 ---> 1 -------------------- 1 ------ X
--1 ---> 0 -------------------- X ------ 1
--1 ---> 1 -------------------- X ------ 0
---------------------------------------------

So, how can I know about the D Flip-Flops inputs?

A D flip flop's Q output follows the state of the D input when clocked. This is no help to your counter, but as an illustration, you can make a D flip flop toggle on each clock by tying the Q^ output to the D input.