Chicken Gizzard - Expert please reply

abhi0697 wrote:Because chickens lack teeth, they need another way to break apart the food they eat before reaching the stomach, and for this reason, chickens have a gizzard in which stones they swallow are used to grind their food.
A) before reaching the stomach, and for this reason, chickens have a gizzard in which stones they swallow are used to grind their food.
B) before it reaches the stomach, and for this reason, chickens have a gizzard in which stones they have swallowed is used to grind their food.
C) before it reaches the stomach, and for this reason, chickens have a gizzard in which stones they swallow are used to grind their food.
D) before reaching the stomach, and for this reason, chickens have a gizzard in which stones they have swallowed is used to grind their food.
E) before it reaches the stomach, and for this reason, chickens have a gizzard in which stones they have swallowed are used to grind their food.

abhi0697 wrote:The reason for E and not C is "The present tense verb swallow should be replaced with the present perfect verb have swallowed in order to indicate that the swallowing occurred before the use of the stones"
Not really convinced as MGMAT SC states that use present perfect for continued action or continued effect of completed action. But the explanation here suggests that occurrence time of two events are different.

abhi0697 wrote:The reason for E and not C is "The present tense verb swallow should be replaced with the present perfect verb have swallowed in order to indicate that the swallowing occurred before the use of the stones"
Not really convinced as MGMAT SC states that use present perfect for continued action or continued effect of completed action. But the explanation here suggests that occurrence time of two events are different.