Final answer:
The sentence 'School-age children and college students were pushed into virtual learning environments in March 2020, with schools closing for unspecified lengths of time' is a complex sentence with one independent clause and one dependent clause.
Step-by-step explanation:
The sentence 'School-age children and college students were pushed into virtual learning environments in March 2020, with schools closing for unspecified lengths of time' is a complex sentence. It contains one independent clause 'School-age children and college students were pushed into virtual learning environments' and one dependent clause 'in March 2020, with schools closing for unspecified lengths of time'. The independent clause can stand alone as a sentence, while the dependent clause cannot.