Step 1: Analyzing the electric field pattern.
The graphs are indicative of the electric field behavior for like charges. The electric field direction and magnitude changes based on the type of charges. The field due to positive charges spreads away from the charge.
Step 2: Conclusion.
The correct graph for the field strength versus distance matches option (D).
Final Answer:
\[
\boxed{\text{(D) Both positive; Q1 positive, Q2 negative; Q1 negative, Q2 positive; both negative}}
\]