Pronoun agreement:

How do you know when to use who or whom?

Who is a subject of a verb.
Examples:
Who let the dog out?
Pat is the person who is always late.

Whom is used as the object of a verb or a preposition.
Examples:
He asked, "For whom does the bell toll?"
Whom did you see entering the building?

Check this site for more information.
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Thanks

http://grammar.ccc.commnet.edu/grammar/pronouns1.htm
Scroll down to Personal Pronouns.

http://www.uottawa.ca/academic/arts/writcent/hypergrammar/pronref.html
Scroll down to Use "who," "which," and "that" carefully.

http://members.cox.net/lenco1/grammarpractice/
Click on Usage Practice at the left, then on Who/Whom.

Basically, if you can rephrase and use "him" or "her" or "them" -- then you need "whom." But if you rephrase and use "he" or "she" or "they" -- then you use "who."

The above is very general; the information in the websites above is more specific.

=)

what is the simple tenses of verbs

The simple tenses of verbs refer to three different forms of a verb: the simple present, the simple past, and the simple future.

1. Simple Present:
The simple present tense is used to express actions that are habitual, general truths, or actions that happen regularly. It is formed by using the base form of the verb.

Example:
- I walk to school every day.
- Dogs bark loudly.

2. Simple Past:
The simple past tense is used to express actions that occurred in the past and are now completed. It is formed by adding "-ed" to regular verbs or using the irregular form of the verb.

Example:
- They played soccer yesterday.
- She ate lunch an hour ago.

3. Simple Future:
The simple future tense is used to express actions that will happen in the future. It is formed by using the auxiliary verb "will" or "shall" followed by the base form of the verb.

Example:
- I will go to the store tomorrow.
- They shall visit their grandparents next week.

Remember that these are just the basic forms of the simple tenses. There are also variations and other forms depending on the verb tense, such as the progressive or perfect tenses. For more information and specific examples, you can refer to the links provided in the previous response.