Question

The students as well as the teacher ______entered the class

Answer 1

the answer is cheerfully or hopefully

Answer 2

The students as well as the teacher have entered the class.

rule of subject verb agreement used here is:

If subjects are joined by 'as well as' the verb must agree with the first subject .

Here,

students (plural) is the first subject while teacher (singular ) is the second subject hence, in respect of first subject that is plural  the verb taken is plural (have instead of has) .

NOTE: the blank place can also be satisfied with HAD.