Answer:
A. Sing
B. Is
C. Was, is, will be
D. Ran, played
Step-by-step explanation:
First, we will define the simple predicate, compound predicate, and complete predicate.
The simple predicate is one verb or verb phrase in the sentence.
The compound predicate consists of two or more verbs or verb phrases that refer to a single subject.
The complete predicate includes all the words in the sentence that give more information about the subject (not only the verb but the words that modify it as well).
The first two sentences are not an issue since we have one verb in each of them (A - sing, B - is). The problem is the last two, which contain more than one verb (C - was, is, will be; D - ran, played), making their predicates compound predicates. Compared to the complete predicate they could be considered simple predicates, but it's best to keep in mind that there is a difference.