How can GPS be affected by EW, and what are countermeasures?

How can GPS be affected by EW, and what are countermeasures?

• A. GPS can be jammed or spoofed; countermeasures include anti-jam receivers, encrypted signals, and use of alternative navigation aids.
• B. GPS is immune to EW; no countermeasures required.
• C. GPS can be enhanced by increasing signal strength from satellites; no countermeasures needed.
• D. GPS only affected by solar flares; encryption not used.

Answer: (A)