Al museo cada lunes a las diez de la manana

I am guessing its "va a" it makes a lot of sense whan u write that it means is will go, this will make the sentence look like El va a ir al museo cada lunes a las diez de la mañana, this means he will go to the museum every monday at 10 in the morning

Hope this helps

It is letter b
los empleados se quejan de no tener un buen sueldo.

Incorrect. the right answer is "su nieto estudia la lecciòn"