Which is the subordinate clause in the sentence?

as the tides rise and fall, the levels of salt concentrations change, and animals must adjust to wide salinity variations.

a. the levels of salt concentrations change
b. animals must adjust to wide salinity variations
c. as the tides rise and fall
d. to wide salinity variations

The subordinating clause in the sentence stated above is:

C.as the tides rise and fall

The clause begins with a subordinate conjunction "as" and contains a subject and verb. Subordinating conjunctions is also referred to as dependent clause because it cannot stand alone and therefore needs the independent clause to express a complete thought.