When a perfectly competitive firm and industry are both in equilibrium
a P=MR=SMC=LMC
b P=MR=SAC=LAC
c P=MR=lowest pt on LAC curve
d all of the above..
If MRTS increases ,then isoquants are concave.
Hence slope increases.
You can do the other way round too...MRTS decreases along an isoquant,so if we go upwards isoqant becomes steeper..
Therefore ans is slope increases.