Notice how the melting curve for wet peridotite occurs at much lower temperatures than the melting curve for dry peridotite at similar depths and pressures. Of course, rocks can also be partially melted by heating them up. Crustal rocks are primarily melted by temperature increases. Determine the primary means of melting that would occur at divergent boundaries, convergent boundaries, and within a plate (intraplate).

In the convergent boundary, as the plate go deeper pressure increases and temperature also and when the pore water will be released they helped in partial melting. So while the condition will be there as at the melting curve, then an increase in temperature will produce huge partial melt due to presence of water. As shown in the above curves of melting curve of wet peridotite.

In the intraplate melting, the pressure is not changing only temperature of the peridotite is changing . So when temperature will increase it will start to melt (As shown in figure).

In divergent boundary the melting occurs due to decompression. There is no role of temperature here . As temperature is almost constant and the rock will come up it will undergo decompression and will produce melt (As shown in fig 3, decrease in pressure results in melting).

the answer is b. apsidal precession