gross profit

which of the following wd cause the gp margin to fall

1. closing inventory is lower than opening inventory
2. some items in the inventory were valued at less than cost.

the text says that 2 is the correct answer.

i chose 1 because:

random numbers:

cogs=50 +100 – 60 = 90
cogs=60 + 100 – 50 = 110

thus when closing inv<opening inv gives a higher cost thus a lower gp.

so where am i wrong?