Please help:

Which sentence uses apostrophes correctly?
A. Martha's new bike was stuck and couldn't nove.
B. Tracy's only brothers' birthday si the day before hers.
C. Walter's childrens' grades have been improving lately.

Let us know what you think.

The first one

Right!

To determine which sentence uses apostrophes correctly, let's analyze each option:

A. Martha's new bike was stuck and couldn't nove.
In this sentence, we have one apostrophe used correctly in "Martha's" to indicate possession. However, there is a misspelling of "move" as "nove."

B. Tracy's only brothers' birthday si the day before hers.
In this sentence, we have an incorrect usage of the apostrophe. The placement of the apostrophe in "brothers'" suggests multiple brothers possessing the birthday, but since "brothers" is already plural, it should be written as "brothers" without an apostrophe. Additionally, there is a misspelling of "is" as "si."

C. Walter's childrens' grades have been improving lately.
In this sentence, we have two incorrect usages of apostrophes. Firstly, "childrens'" should be "children's" to indicate possession of the children. Secondly, there is no need for the apostrophe in "grades." It should simply be written as "children's grades."

Based on these analyses, the correct sentence that uses apostrophes is option A: Martha's new bike was stuck and couldn't move.