אני חושבת שהמפתחות שלי אצלך.

I think my keys are with you.

Breakdown of אני חושבת שהמפתחות שלי אצלך.

• אני: I
• ש: that
• שלי: my
• מפתח: key

Questions & Answers about אני חושבת שהמפתחות שלי אצלך.

Why is חושבת used here?

Because the speaker is female.

In Hebrew, the present tense often agrees with the gender and number of the subject.
So:

• אני חושבת = I think (said by a woman)
• אני חושב = I think (said by a man)

Even though English just says I think for everyone, Hebrew makes this distinction.

What would a male speaker say instead?

A male speaker would say:

אני חושב שהמפתחות שלי אצלך.

The only change is:

• חושבת → feminine singular
• חושב → masculine singular

Everything else stays the same.

What does ש־ mean in שהמפתחות?

ש־ means that.

So:

• אני חושבת = I think
• שהמפתחות שלי אצלך = that my keys are with you / at your place

In Hebrew, this ש־ is attached directly to the next word, so you get:

• ש + המפתחות → שהמפתחות

This is very common in everyday Hebrew.