Answer:
1. el
2. el
3. los
4. la
5. las
6. el
Step-by-step explanation:
1. Boligrafo is masculino ending in -o and is singular.
2. laboratorio is masculino, ending in -o and is singular.
3. Todos is masculino, ending in -o, and estudiantes is plural ending in -s.
4. biblioteca is feminino, ending in -a, and is singular.
5. tijeras is feminino, ending in -a, and is plural ending in -s.
6. periodo is masculino ending in -o, and is singular.
-Hope this helped.