Answer:
simple
Step-by-step explanation:
Simple sentence has one subject and one verb. e.g. I am going to visit a doctor on Saturday.
Compound sentence includes two separate sentences which are connected with a conjunction. e.g. I enjoy watching drama movies, but my sister hates them.
Complex sentence is made of two clauses, one dependent clause and one independent clause. e.g. because I was in a hurry, I had to travel by plane.
The sentence ‘Halley's comet should return in the year 2061’, is a simple sentence.