Step 1: Understanding the Concept
Soil water exists as gravitational, capillary, hygroscopic and combined water.
Step 2: Availability
Capillary water is held in soil pores and is easily absorbed by roots.
Step 3: Compare the options
Gravitational water drains away, and hygroscopic and combined water are held tightly and are unavailable.
Final Answer:
Capillary water is available to plants.
\[ \boxed{\text{(B) }\text{capillary}} \]