Select the answer that best completes the sentence.
mochila es grande.
la
los
las
el

select the answer that best completes the sentence.
cuaderno es blanco.
la
los
las
el

select the answer that best completes the sentence.
cuadernos son míos.
la
los
las
el

select the answer that best completes the sentence.
dame lápiz.
un
unos
unas
una

select the answer that best completes the sentence.
esa es pizarra.
un
unos
unas
una

La, los, las and el all are Spanish definite articles. So you may use a definite article when thinking that the reader or listener knows which particular thing or person are being described. Definite articles must match the noun they describe in both gender and number. Since mochila is a feminine singular noun, we choose the definite article that matches this form, which is la. Finally:

La mochila es grande (The backpack is big)

La, los, las and el all are Spanish definite articles. According to the previous definition, we know that cuaderno is a masculine singular noun. Accordingly, we choose the definite article that matches the masculine singular form, which is el. Finally, we can write and translate this sentence as follows:

El cuaderno es blanco (The notebook is white)

We know that cuadernos is a masculine plural noun because it ends in s and according to the previous definition, we must choose the definite article that matches the masculine plural form. Accordingly, we take los as the correct form to be used here. Finally, we can write and translate this sentence as follows:

Los cuadernos son míos (The notebooks are mine)

Un, unos, unas and una all are Spanish indefinite articles and this is used to refer to a particular person or thing whenever the reader or listener doesn't know which one is being described. Since lápiz is a masculine singular noun, we choose the indefinite article that matches this form, which is una. Finally:

Dame un lápiz (Give me a pencil)

Since pizarra is a feminine singular noun, we choose the indefinite article that also matches this form, which is una. Also, esa is a demonstrative adjective that indicates indicates something that is further from the speaker but, however, it can be close to the listener. Finally:

Esa es una pizarra (This is a blackboard)