Question

which of the following is a compound sentence? because robots are machines that can perform complex tasks, a machine is not considered a robot if it performs only simple tasks. robots can perform different tasks, but they are limited by the number of tasks they can perform at one time. robots that can perform simple tasks are becoming very popular. since the word “robot” refers to machines that can perform complex tasks, but is limited to machines whose tasks are not controlled by humans.

Explanation:

A compound sentence has two independent clauses joined by a coordinating conjunction (such as and, but, or). In "Robots can perform different tasks, but they are limited by the number of tasks they can perform at one time", "Robots can perform different tasks" and "they are limited by the number of tasks they can perform at one time" are independent clauses joined by "but". The other sentences are complex sentences (with dependent - clauses starting with "because", "since") or simple sentences.

Answer:

Robots can perform different tasks, but they are limited by the number of tasks they can perform at one time.