在GMAT语法中，"just as"和"as"都可以用作连词，但它们的用法略有不同。

"Just as"通常用于比较两个事物或情况，表示它们在某些方面是相同的。例如：

- Just as a plant needs sunlight to grow, a student needs knowledge to succeed.
- Just as a car needs fuel to run, a person needs food to live.

"As"通常用于表示两个事物或情况之间的关系或条件。例如：

- As the weather gets colder, people tend to stay indoors more.
- As a result of the pandemic, many businesses have had to close.

总的来说，"just as"更强调两个事物之间的相似性，而"as"更强调它们之间的关系或条件。