Verb Tenses

Here the tense shift is “asked”, that is the past-tense, the corrected sentence is,

The instructor explains the diagram to students who ask questions during the lecture.

About noon the sky darkened, a breeze sprang up, and a low rumble announces the approaching storm.

Announces is the present tense. It should be,

About noon the sky darkened, a breeze sprang up, and a low rumble announced the approaching storm.

Yesterday we walk to school but later rode the bus home

Yesterday we walked to school but later rode the bus home.

General guideline for tense shift is:

Do shift tense to indicate a change in time frame from one action or state to another.

The children love their new tree house, which they built themselves.

Before they even began deliberations, many jury members had reached a verdict.

Workers are installing extra loudspeakers because the music in tonight’s concert will need amplification.