C is correct. When using the FIFO inventory method, the ending inventory, the cost of goods sold, and the gross margin are the same under either the perpetual or periodic methods. The use of a perpetual or periodic system makes a difference under the weighted average and LIFO methods. 

A is incorrect. When using the FIFO inventory method, the cost of goods sold, and hence the gross margin, are the same under either the perpetual or periodic methods. 

B is incorrect. When using the FIFO inventory method, the cost of goods sold, and hence the gross margin, are the same under either the perpetual or periodic methods. Under either method the oldest items are sold first. The first sale is 550 at $7.50. The next sale is 450 at $7.50  + 150 at $7.60. The perpetual and periodic methods make a difference under weighted average and LIFO.

B is correct. Under IFRS, the inventory would be written down to its net realizable value ($4.1 million); under US GAAP, market value is defined as current replacement cost and thus would be written down to its current replacement cost ($3.8 million). The smaller write-down under IFRS will reduce the amount charged to the cost of goods sold compared with US GAAP and result in a lower cost of goods sold of $0.3 million.

 A is incorrect. The write-down is larger under US GAAP, so IFRS gross profit would be higher, not lower. 

C is incorrect. IFRS and US GAAP define market differently. As current replacement cost (US GAAP definition is lower than NRV) the effect is not the same.