some phase transitions require an input of heat, such as ___ Other phase transitions require heat to be released such as

1 a

2 d

3 a

4 c

explanation:

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.