The question contained in the attachment asks for you to identify the kind of relationship between the two organisms and to give justification for that designation. Let's start with a definition of the kinds of relationships that can exist between organisms. To find biological definitions I would suggest online biological dictionaries as well as wikipedia.com.

Mutualism- a type of symbiosis where two or more species living in close proximity derive benefit ( nutrients, protection, or other life functions) from each other. All organism derive benefit. Reference http://www.biology-online.org/dictionary/Mutualism

Commensalism- a type of symbiosis where two or more species live in close proximity of each other and one is unaffected by the presence of the other while the other benefits from the relationship. Reference http://www.biology-online.org/dictionary/Commensalism

Amensalism- a type of symbiosis whereby one organism is negatively affected by the presence of the other while the other is unaffected. Reference http://en.wikipedia.org/wiki/Amensalism

Now let's look at the interactions in question:

1. Epiphyte plants and trees- an epiphyte is a plant that grows while attached to another plant. They rely on their host for support (generally not harming the host though this may occur in rare circumstances; a parasitic plant like mistletoe is not an epiphyte). Because the epiphyte recieves a benefit while the host is rather unaffected this is an example of commensalism. Reference http://en.wikipedia.org/wiki/Epiphyte

2. Mycorrhizal fungi and plants- in this interaction the fungi receive sugar from the plant while the plant is aided by the fungi in absorbing minerals and water.This is an example of mutualism. Reference http://en.wikipedia.org/wiki/Mycorrhizal_fungi

3. Barnacles and whales- in this relationship the barnacles use the whales for a support structure and motility that aids in food finding while the whale is largely unaffected. This is an example of commensalism. Reference http://library.thinkquest.org/J001418/barnacles.html

4. Flowering plants and hummingbirds- in this relationship flowering plants attract hummingbirds by providing them with nectar. In exchange the hummingbirds unknowingly spread the plant's pollen. This is an example of mutualism.

5. Ants and acacia tree- in this relationship ants are provided with protection for the acacia from leaf-eating insect while the ants receive nectar and structures at the tips of the leaves. This is an example of mutualism. Reference http://en.wikipedia.org/wiki/Acacia_tree.