Answer:
B. While you were at practice, we ate ice cream.
Step-by-step explanation:
A complex sentence contains one independent clause and at least one dependent clause. A compound-complex sentence contains more than one independent clause and at least one dependent clause.
In this sentence, 'While you were at practice, we ate ice cream', the dependent clause began with a subordinating conjunction which was while. This clause was also seperated by a comma and transitioned into another subject.