We can reasonably complete the sentence as follows: They also have challenges.
How to complete the sentence
To complete this sentence, we can say get an idea of the subject because of the singular verb, have. As a rule, singular verbs would go with plural subjects. Also, the wording suggests that the challenges are not just one but many. So, an ideal way to complete the sentence would be: They also have challenges.
There is a subject-verb agreement that sees the plural 'they' going with the singular 'have' and the object, 'challenges.' So, the sentence can be completed as specified above.
Complete Question:
Complete the sentence: ------------also have challenge