This question is a simple interrogation of correct pronoun usage. The only possible correct answer is thus "her" since "Kathy" is the object of the second main clause. 

In this sentence, the subject/noun that is being replaced is Rebecca. It can be assumed that Rebecca is a female name, so the most appropriate pronoun to replace it is "she." "They" refers to a group of people, "he" is used for males, and "it" would refer to something previously mentioned or easily identified, so in this instance, "she" is the best fit.

In this sentence, the subject/noun that is being replaced is "the nurses". It can be assumed that "the nurses" is referring to a group of nurses or multiple nurses because of the -s ending, so the most appropriate pronoun to replace the noun is "they." "They" refers to a group of people, "he" is used for males, "she" is used for females, and "it" would refer to something previously mentioned or easily identified, so in this instance, "they" is the best fit.

In this sentence, the subject/noun that is being replaced is "the yogurt". It can be assumed that "the yogurt" is something recognizable, and because of the first sentence, it is something that has been made known, so the most appropriate pronoun to replace it is "it." "They" refers to a group of people, "he" is used for males, and "it" would refer to something previously mentioned or easily identified, so in this instance, "it" is the best fit.

In this sentence, the subject/noun that is being replaced is Gregory. It can be assumed that Gregory is a male name, so the most appropriate pronoun to replace it is “he.” The sentence mentions that the dog is "his" dog which also hints that Gregory is a male. “They” refers to a group of people, "she" is used for females, “he” is used for males, and “it” would refer to something previously mentioned or easily identified, so in this instance, “he” is the best fit.

This sentence is past tense because it's talking about something that happened yesterday. 

When a sentence is past tense, we add -ed to the verb. The verb from the answer choices is "walk", so the correct answer is "walked". 

Yesterday I walked to school. 

This sentence is about something that is going to happen in the future. We know this because of the word "tomorrow". 

When a sentence tells about the future, we add "will" before the verb. The verb from the answer choices is "walk", so the correct answer is "will walk". 

Tomorrow I will walk to school. 

This sentence is talking about something that is taking place right now. This is a present tense sentence.   

When a sentence is in present tense, the verb normally has no ending added to it. The verb from the answer choices is "walk", so the correct answer is "walk". 

Today I walk to school. 

When a sentence is past tense, we add -ed to the verb

When a sentence tells about the future, we add "will" before the verb. 

When a sentence is in present tense, the verb normally has no ending added to it.

This sentence is past tense because it's talking about something that happened yesterday. 

When a sentence is past tense, we add -ed to the verb

When a sentence tells about the future, we add "will" before the verb. 

When a sentence is in present tense, the verb normally has no ending added to it.

This sentence is past tense because it's talking about something that happened yesterday.