On the psychrometric chart, a heating and humidification process appears as a line that is (a) Horizontal

Question:

On the psychrometric chart, a heating and humidification process appears as a line that is
(a) Horizontal to the right
(b) Vertical upward
(c) Diagonal upwards to the right (NE direction)
(d) Diagonal upwards to the left (NW direction)
(e) Diagonal downwards to the right (SE direction)