French language Q&A Forum

I have 2 questions
1-
can I use indirect object or direct object  before the verb for "penser à" when I talk about people? 
and what is the rule for 
Je pense à Lui(tom) 
je lui pense or je le pense?? (does it work with any of them?)
2-how can I inverted imperatif with penser à for people
pense à moi  or pense moi (whicj one is true?)

Why sometimes in passé composé the conjugated verbs in plural end with '' s '' and sometimes don't end with an '' s ''. 

Ex: '' Elles sont devenues méchantes à cause de toi.'' 

Ex: '' Ils ont vendu (vendre) des croissants dans la rue.'' 

When to put an '' s ''? 

Thanks in advance :) 

Is 'Ils s'ont enrichi grâce à leur histoire d'amour, a reasonable alternative

to

Ils sont devenus riches grâce à leur histoire d'amour.

Note: Collins on-line came up with s'enrichir = to get rich

Why do we use "c'est aussi" to say "it was"?  Also why "c'est le premier octobre" to say "it was the first of October"?

Is it correct that simply the duration itself can express a duration in specific time frame, and 'pendant' is optional? For example: 

1) J'étais là pendant 45 minutes = J'tais là 45 minutes

2) Je me brosse les dents trois minutes à chaque fois = Je me brosse les dents pendant trois minutes à chaque fois

3) Nous sommes restés à Tokyo pendant 10 jours = Nous sommes restés à Tokyo 10 jours

4) Combien de temps vous avez resté =  Pendant combien de temps vous avez resté?

Thank you. 

I can't understand that..really i'm unable to understand..please help me..because next year i'm doing A/L

does participe passé agree with direct object when "on" is the subject of the passive sentence.
for example  on l'a regardée (she was watched)(la is feminin article)
ı wish your helps thanks

This lesson is too complex and far too much information is posted. Can you split it up into five or six different lessons? I am not learning well with this current set up. 

Il me semble un peu injuste de ne pas offrir les chiffres écrits en mots comme option.