Step 1: The findings described - burning (singeing/scorching), blackening (smoke soot), and tattooing (unburnt and partly burnt powder grains driven into skin) - are the classic features of a close-range (close shot) firearm entry wound.
Step 2: These flame, soot, and powder effects can reach the skin only when the muzzle is near the body. As the range increases beyond about a foot or more, soot and powder no longer reach the skin, so a distant shot shows none of these, ruling out options c and d.
Step 3: A grease/dirt collar (a black ring of dirt and lubricant wiped off the bullet) is a feature of the ENTRY wound, not the exit wound. Exit wounds are typically everted and lack burning, blackening, tattooing, and a dirt collar, ruling out option b.
Step 4: Combining close-range powder effects with an entry-type dirt collar, the injury is a close shot entry wound.